Introduction

Posadas, Argentina and Encarnación, Paraguay are cities with developments that mutually imply each other and connected socio-urban processes. They have a sustained multipurpose relationship and undergo reciprocal conditioning. In addition, these cities have several shared characteristics, which integrate them in a unique way through a cross-border conurbation. First, these are medium-sized border cities; one of them is the capital of the province and the other of the department, respectively, they have developed a conurbation process, driving the urban dynamics of smaller neighboring cities. Secondly, another unique feature refers to the opening of the San Roque González de Santa Cruz International Bridge, which connects the two cities. This bridge created an international urban corridor, making it possible to overcome the adversities of the Paraná River and to develop a bi-national transport system (taxi, motorcycle-taxi, urban buses, train, etc.) that connects the two nations’ inhabitants on a daily basis. The third characteristic is that both cities were affected by the Paraná River reservoir and the consequent infrastructure system of coastal defenses of the Yacyretá hydroelectric dam. These works entailed abundant urban renewal and enhancement actions on both banks of the river.

Finally, in terms of socio-economic exchanges, Posadas and Encarnación definitely possess some of the most marked characteristics of twin cities: proximity, development of local interactions, and simultaneous competition and cooperation relations. Due to such processes, the relationship between these cities has special features. The nature of these cities, in conjunction with other events, revives the contemporary debate regarding border cities.

Without a doubt, the special relationship between Posadas and Encarnación harkens back to the past. These cities were born through the same socio-historical process and, since their beginnings, have been intimately linked to the border, sharing fluid interactions and close socio-economic and cultural ties. However, as I will try to demonstrate, today, their unique socio-spatial reconfigurations, added to the spaces of flows and opportunity structures, highlight their complementary characteristics and rationalities.

The set of characteristics of Posadas and Encarnación can be interpreted based on the widespread model of twin cities: cities that, despite lacking a common government, share economic, cultural, neighborhood and complementarity relations, affecting each other and generating interdependencies, mutual constraints, and a specific form of inter-urban articulation. Therefore, it is important to introduce a brief discussion of the processes and theoretical-conceptual dimensions involved in the approach to this phenomenon.

Border Cities: Conceptual Dilemmas and Approximations

The denomination of cities located at international borders has increasingly changed, namely: twin cities, pair cities, border cities, bi-national cities, double cities, cross-border cities, mirror cities, etc. (^{Alegría, 2008}; ^{Buursink, 2001}; ^{Carrión, 2016}; ^{Vergel-Tovar, 2008}). The existence of a border and of a “pair” city is sine qua non for the emergence of these cities and their future characteristics on either side of the border. One of the features of so-called twin cities is having cross-border flows (^{Steiman, 2012}). These flows affect the conditions in which their residents live and offer opportunity structures associated with residential location that impact population growth.

It is worth mentioning that while approaching these dilemmas conceptually, the article’s criterion of theoretical discussion is to combine criteria based on the convergence of significant contributions, regardless of the dissimilar proposals of different authors, in order to 1) understand the generalized model of twin cities and 2) describe the empirical properties and characteristics of the case analyzed and its specificities.

The definition of twin cities upheld by the media has led to much confusion by presenting it as a simile or as the cities having an identical nature. However, it is precisely this feature, the cities’ appearance as “equal,” that should not be highlighted because there are no cities that are structurally identical or perfectly equal¹. A more widely accepted definition states that twin cities are part of an international border, are geographically close and share local interactions (^{Kearney & Knopp, 1995}), constituting an urban continuity. This concept also relates to the notion of interrelated cultures, economies and societies (^{Zavaleta, 1986}). For ^{Carrión (2016}), “twin or mirror” cities would not exist, per se, if not for the link with the “other side,” creating an interconnection at the edges of states. Thus, it is often the case that these cities constitute contact points between nations enabling commercial exchange and mutual use. Making use of a biological notion and in line with this perspective, the concept of the twin city implies that there is a symbiotic relationship of equality between both cities (^{Peña, 2008}). Needless to say, such an equality refers to a complementarity relationship through an associative link.

Although the notion of twin cities originally referred to a type of urban border agglomeration, in recent times, this concept has been refined and significantly developed by many social scientists who analyze international urban pair cities. Thus, for ^{Tambi (2016}), twin cities are border cities, adjacent to each other, with neighborhood conditions subject to integration and stable bilateral ties. Consequently, they can develop a common agenda. Twin cities have also been described by occasional visits among their inhabitants, who establish stable contacts on the other side of the border (^{Mikhailova, 2013}).

Publications on border cities discuss a wide range of topics, from urban development, governance systems and trade relations up to inter-urban dynamics. Urban continuity-discontinuity has been debated when delimiting these cities. Some perspectives assert that twin cities may present a unified urban fabric with the city of the neighboring country, being either spatially continuous or discontinuous. Another angle of debate relates to physical spatiality, linked to a set of flows, networks and relations of a social, economic, cultural, political and environmental nature, established between two or even more cities belonging to different countries (^{Zárate, 2012}).

The existence of a border city is intimately linked to border activities, and its urban dynamics interact with the administrative and political margins of countries. Twin cities do indeed face each other across an international border and, therefore, have a particular relationship. According to Ehlers, ^{Buursink and Boekema (2001)}, border cities, after years and perhaps centuries of interrelationships, often find themselves existing in a delicate balance between competition and cooperation, independence and dependence.

Other conceptual contributions, also relevant to study the phenomena analyzed here, refer to bi-national conurbation processes and their socio-urban and demographic implications (^{Bustamante, 1981}), or to the existence of urban bi-national complexes (^{Carrión, 2016}). From an interesting perspective, ^{Dilla (2008}) proposes the notion of cross-border urban complexes (CUC) to analyze a series of circumstances: a) shared representation of a mutual need, b) geographic proximity, c) interdependent economic reproduction, d) sustainable primary social relations among inhabitants, e) shared socio-cultural and urban services, and f) existence of institutional relations, including the State and civil society². From my point of view, this perspective is particularly relevant as a definition of indicators that allow understanding “some” manifestations of the cities in a border context.

Beyond the physical aspect, which entails a perceptible territorial dimension of close cities, it is important to analyze how these cities merge with the border and the economic processes and socio-cultural products derived from them. The cross-border issue is central; the cities themselves bear the imprint of the border, foreshadowing its nature and conditioning its evolution. As Herzog (cited on ^{Dilla, 2015, p. 46}) states, “...border cities have become so connected functionally that their futures are inescapably linked, regardless of whether national governments establish formal procedures to influence border problems.”

Beyond the relevance of the different theoretical contributions presented here, we follow Steiman’s singular point of view (^{Steiman, 2012}). For this author, twin cities are defined as urban centers located on either side of an international border, whose interdependence is often greater than the role that each city may have in its region or national territory. Similarly, we agree with ^{Vergel-Tovar (2008)}, who argues that it is not a matter of similarities between built environments or institutional frameworks but of social spaces created by border residents that generate the symmetric and asymmetric processes that define the characteristics of the border.

In another work (^{Souza & Brites, 2017}), we argued that beyond global and contemporary urban processes, cities located in international borders experience socio-urban processes of unusual complexity and variability. In other words, border cities acquire a specific configuration and dynamic in their development and consolidation, including built urban environments, their inhabitants’ practices, legislation and international policies.

Leaving the literature proposed here aside, we believe that cities in transborder contexts blend several conditions and situations that, beyond economic relations (symmetric, asymmetric, changing), interact with urban processes, policies (laws) and the uniqueness of opportunity structures that may arise on either side of the border.

Specifically, Posadas-Encarnación share a series of characteristics that provide us with material for supporting the idea that they may be regarded as twin cities, comprising a cross-border conurbation with unique situations and relationships. This argument is based on the following reasons:

Far from being an “integrationist” proposal of twin cities, I argue that Posadas and Encarnación have relational processes that are characterized by asymmetries and differences regarding the socio-economic and cultural spheres but also by complementary and regular exchange rationales, cross-border flows of commerce (both formal and informal), job opportunities, health and education services, urban transportation systems, and infrastructure networks, among others. This scenario provides us with a complex urban cross-border reality (Figure 1).

Source: Prepared by the authors based on Google Earth.

Figure 1 Posadas and Encarnación: Urban nuclei in the context of border proximity 

Study Methodology

This study presents original information on a case of medium-sized border cities with unique features in the regional context. This study is exploratory, anchored in a descriptive and diachronic approach that presents empirical evidence allowing the understanding of these conurbations based on the model of twin cities³. To complete this research, different sources of information were collected and analyzed, namely: official and non-official documents and files, news from local newspapers, bi-national treaties, programs and policies for development, municipal laws of both cities, etc. Additionally, during the field phase, semi-structured interviews were conducted with several informants, including customs officers, bus drivers, taxi drivers, paseros (small-scale cross-border peddlers), traders, street vendors, and, more specifically, conversations with inhabitants of both cities and discussions with other researchers.

At a general level, this research furthered questioning in order to understand the dynamics of relational processes, exchanges and complementarities between the two cities. In this sense, research turned to a comparative analysis on various dimensions referring to the international bridge, changes in the urban space, flows and mobilities, exchange dynamics and the structures of cross-border opportunities, among other socio-urban processes, that take place in the cities of Posadas and Encarnación.

The Transformation of Posadas and Encarnación

The Bridge Effects

Posadas and Encarnación’s border locations are key for the historic and fluid economic and socio-cultural exchange between both cities. This longstanding exchange took place first through the river, using boats (Argentine-Paraguay flagged boats) and ships that crossed the Paraná River. Such modes of transport became obsolete after the inauguration of the International bridge in 1990 (Figure 2).

Source: Prepared by the authors based on Google Earth.

Figure 2 Urban and border proximities in Posadas and Encarnación. 

After its construction, which began in 1983, not only were significant expectations raised at the regional level, but there was also great investment in infrastructure work and labor. The San Roque González de Santa Cruz International Bridge⁵ has a total length of 2 550 meters and consists of a rail and road viaduct built on the Paraná River.

This mega construction was historically sought by both countries and was developed in parallel with the Yacyretá dam, which, in conjunction with regional articulation and integration policies within the framework of the Southern Common Market (Mercado Común del Sur-Mercosur), has been much anticipated. In addition to the bi-national treaties involved in its construction, shortly after its opening, the bridge enabled an unprecedented territorial articulation between both cities. This new configuration constituted a more agile and direct option for the movement of people, goods and information than the service provided by traditional boats (^{Báez, Brites & Espinosa, 2013}). In other words, as a bi-national infrastructure, the bridge increased and stimulated socio-economic and cultural relations between Posadas and Encarnación.

Since the inauguration of the International Posadas-Encarnación Bridge, interrelation has been more pronounced, accelerating everyday contact between residents of both cities. Trade asymmetries, the development of a labor market with differential advantages, daily border crossings of thousands of people, the implementation of a Border Neighborhood Transit office, a vast informal market linked to textile, food and electronic products, and the availability of an urban transport system stand out among other aspects that provide this conurbation with unique characteristics. Toward mid-2017, Argentina’s National Directorate of Migration (Dirección Nacional de Migraciones, Argentina) confirmed that, on average, 45 000 people use the international viaduct that connects Posadas and Encarnación on a daily basis.

The bridge exists within a cross-border space where a growing number of people live, with coercive laws at the national and municipal levels controlling border crossing. This situation has given rise to new intergovernmental challenges regarding the jurisdictions of both cities. As ^{Vergel-Tovar (2008, p. 362)} states:

The coexistence of border cities may cause common problems for both urban areas that can be solved through cooperation between the two cities or may create scenarios in which they compete to offer services in the context of a global market economy.

An unusual fact points to the emerging importance of the bridge. Every day, inhabitants of Posadas-Encarnación tend to inquire about it: knowing how transit will be across the bridge is perhaps more important than the weather forecast for that day. In other words, the bridge is a supranational infrastructure, shared locally by Posada and Encarnación residents, constituting a living urban space. Furthermore, it enables and constitutes the way through which citizens encounter dense inter-urban, commercial, labor and survival relations, among others.

Back-and-Forth Relations and Exchanges

Posadas and Encarnación, as cross-border urban spaces, are complex scenarios that represent a challenge in regard to understanding social interrelations, interdependency links and complementary processes of socio-urban articulation. Geographical proximity has socio-spatial effects on both cities, while enabling opportunity structures on either side of the border: capitals, jobs, land, public and/or private services, shops, etc.-these items add to the long history of interconnection and shared socio-cultural processes.

In many cases, crossing the border, visiting and getting to know the neighboring city becomes part of daily life and a necessity. In addition to traditional small-scale trade by Paraguayan paseros (^{Linares, 2017}), it is common to see Paraguayan citizens working in construction, domestic service, commerce, selling products door to door, resale and/or purchase of goods, etc., in Posadas. Similarly, Argentinian citizens come to Encarnación to purchase products (textiles, electronics, bazaar goods, spare parts, etc.), either for their own consumption or for resale as a strategy to maximize income. To a lesser extent, crossing the border may become a strategy to find employment in jobs that demand higher qualifications (professional services, teaching, and others)⁶.

Many of these interrelationships are not exclusively economic; sometimes, they entail parental and/or family relationships⁷. Fundamentally, since border areas represent heterogeneous realities, they constitute sociability spheres in permanent transformation (^{Benedetti, 2011}).

Different periods and economic circumstances (which fall outside the scope of this research) have influenced the variable flows and exchanges between the two cities, enabling new and unique interactions among citizens. For example, during the 90s -to name only one stage-, the exchange rate gap between pesos, dollars and the guarani caused an asymmetry in rate exchange. In this context, the possibility of choosing the differential advantages offered by the border monetary system created various strategies linked to activities that transcended labor dimensions and trade. One example emblematic of such strategies was the case of Posadas inhabitants who moved to Encarnación but kept their jobs in Posadas, or that of young people from Posadas who began their university studies in Encarnación, or Encarnación builders who worked in Posadas. As a common practice, all of them crossed the bridge daily.

After the bridge united these cities, their socio-economic processes have improved intermittently and complementarily on both sides of the border. Interests and rationales behind purchases and sales have been remarkably selective, ranging from fuel, cement, food and medicines in some cases, to paint, clothing, cigarettes and whiskey in others. We are talking about purchasing strategies on both sides, depending on the products. This process has, in many cases, encouraged favoritism among sellers and buyers. Thus, the strength of these relationships revolves around the economy, keeping in mind that these relationships merge with a series of illegal, legal and quasi-illegal practices linked to border traffic.

As border settlers, Posadas and Encarnación inhabitants are subject to both Border Neighborhood Transit and Border Neighborhood Traffic agreements. Despite being bi-national, the first is not an agreement between States but between municipalities (^{Organización Internacional para las Migraciones [OIM], 2018}) and authorizes entry, stays and movement for 72 hours and a radius of up to 50 kilometers in both cities. This agreement also allows access to a Border Neighborhood Transit credential (TVF, for its Spanish acronym)⁸. The Border Neighborhood Traffic regime is a simplified customs procedure that allows acquiring (purchasing) products for personal and household use, including clothes and garments, with a quota of 150 U.S. dollars per person each month⁹. However, accounts of people who cross the border state that this agreement is not an effective mechanism of control, and there are recurrent evasion strategies (buying and bringing products illegally, hiding goods or not declaring them, etc.).

As illustrated in Figure 3, in recent years, the number of people who cross the international bridge has significantly increased. Many visitors come from other cities or come on shopping tours; however, the movements due to the Border Neighborhood Transit between Posadas and Encarnación amount to 55% of traffic (^{OIM, 2018})¹⁰. This specific kind of movement refers to everyday trips in both directions, motivated by activities, social relations, multiple exchanges and other needs.

Source: Prepared by the authors based on National Directorate of Migration (^{Dirección Nacional de Migraciones, 2017}).

Figure 3 Evolution of the annual migratory movements between Posadas and Encarnación 

Many automobiles and motorbikes with Paraguayan license plates can be observed on a daily basis in Posadas. These people are involved in various activities: crossing goods, freight, retail, domestic services, etc., embodying one aspect of commuters, as described by ^{Ojeda (2008)} and ^{Herzog (1990)}, in reference to workers who live on one side of the border but work on the other and who carry out important inter-city and cross-border commutes¹¹. These everyday trips from one city to another, facilitated by a shared urban transport system, show new ways of relating as well as adaptation processes to the new socio-urban, economic, and cultural conditions derived from the relationship between these border cities.

Markets in Posadas and Encarnación streamline forms of mobility based on intricate and complementary trade relations that are not exempt from conflicts and tensions. In some cases, Posadas traders demand actions in response to the disadvantageous commercial competition with Encarnación and its citizens, who sell, buy and access services in Posadas. In general, citizens -on both sides of the border- ask for more freedom and fewer controls to cross the border. In other words, commercial and service asymmetries are not seen at all as serious problems but as an opportunity structure that enables access to differential goods and services.

Currently, both Encarnación and Posadas feature services, leisure and entertainment spaces that go beyond motivations, magnitudes, senses, complexities and jurisdictions and represent living spaces in use by inhabitants: hospitals, large shops, beaches, restaurants, discos, casinos, green spaces, cultural events, carnivals, etc. All these experiences resulting from crossing the border, sharing services, knowing places, and participating in socio-urban centers open a variety of cross-border social relations¹². In other words, mutual interdependence relations are embodied in customary and recurrent expressions among its citizens: What would we do if Posadas wasn't on the other side! Going to Encarnación is almost a necessity!

Mobility and Spaces of Flows. Living the Border Locally

Regarding mobility, the consolidation of the Posadas-Encarnación urban districts and the intensification of their activities entails an increase in the use of transport not only in urban center-periphery journeys but also from these areas to neighboring cities and/or their border centers. There are two international bus companies that joined the bus stations in Posadas and Encarnación, which contributes considerably to increased inter-urban mobility (Figure 4).

Source: Prepared by the authors based on Wikimapia.

Figure 4 Cross-border flows in Posadas-Encarnación 

In the last 10 years, the interrelation between the two cities has become more pronounced. A growing number of people cross the bridge, and there are endless rows of cars and buses. Similarly, people from other places who gather in the hope of reaching Encarnación to take shopping tours also add to this scenario¹³. Immigration and custom controls, added to the recurring long waits, have drawn the focus of the citizens from Posadas and Encarnación who need to cross the border daily. For this reason, traffic on the bridge constitutes the focus of daily news and information in the media¹⁴.

As the number of people crossing the border has increased, claims and conflicts have arisen among different social actors (carriers, customs officials, soldiers, passengers, taxi drivers, motorcycle-taxi drivers, etc.), which has sparked the search for better urban mobility conditions across borders. In 2015, a bi-national train service was implemented to increase the frequencies of trips and reduce waiting times. This service supplements international urban transport. The train, with capacity for 190 passengers, goes back and forth from one station to the other on a ten-minute route each way. However, despite the measures implemented, the dense volume of vehicles and the number of people on the bridgehead is increasing (Table 1). Currently, new alternatives to enhance cross-border mobility are being discussed, including the construction of more border boxes, expanding train cars, implementing continuous shifts and built-in controls, etc.

Table 1.  Passengers transported by train between Posadas and Encarnación  

Years	Passengers mobilized
2015	832 042
2016	1 407 545
2017	1 508 718

Source: Comisión Nacional de Regulación del Transporte (CNRT), 2017.

In recent times, despite high concurrency, crowding and congestion at the border, thousands of people have continued to cross the bridge on a daily basis, even several times a day, taking advantage of the Border Neighborhood Transit regime through repeated, short journeys to bring goods in and out of the city and the country. This fact has drawn attention since, in addition to unveiling singular practices, it highlights the intensity of the interaction and exchanges of material and human resources.

Despite the intermittent discontent of traders from Posadas due to commercial asymmetries with Encarnación, most residents of both cities demand improvements in physical infrastructure and inter-urban communication routes. These claims recently became visible through the movements against the so-called “wall of shame.” This wall (5 meters in height and 1 500 meters long) was built in the center of the Posadas border in an attempt to toughen immigration controls and customs procedures. However, after two years, continuous complaints forced the demolition of part of the wall in order to improve communication between the two cities.

Bilateral Cooperation Relations

The Border Neighborhood Transit and Traffic regimes, which mainly focus on the economy, are only a visible part of the bilateral cooperation agreements; however, both cities occasionally establish local cross-border links (with varying degrees of formalization) in order to solve incumbency issues in the management of border and inter-urban relations.

Lately, there have been many occasions on which Posadas and Encarnación have developed common agendas to unify control criteria, streamline border crossing, avoid long waits, improve relations, etc. The complexity of these problems has led not only to the creation of inter-municipal cross-border cooperation links (among local authorities) but also to the development of institutional links at different scales, ranging from the Chamber of Commerce and Industry of Posadas [Cámara de Comercio e Industria de Posadas], the Governorate of Itapúa, Ministries of Foreign Affairs (Foreign Trade), and Customs, up to the Yacyretá Bi-national Entity, frequently involving the private sector and other intermediary institutions.

Although integration mechanisms have long been in force, bilateral relations manifested more readily after the formation of the Posadas-Encarnación Integration Committee in 2013¹⁵. In this inter-institutional agreement, issues regarding the Border Neighborhood Traffic agreement and integration were discussed through commissions that addressed problems relating to migration, transport and customs, trade and tourism, police cooperation and security, culture and education, social development and health. In addition, specific agreements of joint epidemiological surveillance, health care control and improvement of infrastructure in the border limits were created.

The ebbs and flows in the intensity of the relationship and inter-urban flows between Posadas and Encarnación revolve around economic fluctuations and the exchange rate disparity between Argentina and Paraguay. This process gives rise to issues related to pendular mobility in both cities, resulting in frequent complaints, protests and petitions to authorities (on both sides) to accelerate the slow process of border crossing. More recently (December 2017), Paraguayan authorities have again heard the claims of Encarnación citizens, and through the Ministry of Foreign Affairs have convened the Argentine authorities with dependency in Posadas to strengthen bilateral commitments in terms of infrastructure, logistics, migration, consular formalities, customs controls and other activities carried out at border crossings for the international bridge.

It is interesting to note that the diplomacy of these twin cities differs from the interests and agreements of the states to which they belong. I assume that bilateral agreements between Posadas and Encarnación are an instrument of vital importance to generate “rapprochement and integration.” In the unusual resulting process, states become closer in the background in response to the necessary proximity relationships between these cities, where local problems help bring national governments together (Figure 5).

Source: Prepared by the author.

Figure 5 Scheme of inter-urban relations between Posadas- Encarnación 

Changes in the Space and New Socio-Urban Processes

Since these are growing conurbations, it is impossible to analyze the socio-spatial transformations of Posadas and Encarnación without referring to the effects of the Yacyretá Dam. The significance of the dam is due not only to changes in the urban morphology of these cities (waterlogging and disappearance of vast areas) but also to the exponential development of large public works of infrastructure refitting (coastal defenses, environmental treatment, construction of residential complexes, relocation of thousands of families). The poorest areas of Posadas and Encarnación, found on the low coasts of the Paraná River and other spaces next to the urban centrality, have been relocated to other distant points in both cities.

The changes in the new riverfront, the characteristics of the coastal constructions, the spaces available, and the new processes of segregation and socio-spatial differentiation have caused the urban planning of these cities to experience the same socio-spatial processes. Twenty years ago, not only did these cities present a more unified urban fabric, their territories were also more compact and dense. Today, urban areas have spread due to population growth, the processes of displacement toward the periphery and the creation of new neighborhoods that multiply in isolation as enclaves without adequate linkage or connection with other areas.

The reconfiguration of the urban fabric in both cities has resulted in new centralities, in spaces of high economic and symbolic value, and in new peripheries (^{Brites, 2014})¹⁶. Population removal and coastal works have given rise to varied urban-renewal interventions: provision of large seafronts, squares and green spaces with urban equipment, arborization of the coastal landscape, etc. After this process, sectors with the greatest purchasing power contested other social sectors, occupying spaces as the environment improved due to the public works created. In other words, Posadas and Encarnación simultaneously transformed their urban spaces as a result of the creation of Yacyretá.

The main problems in territorial terms relate to the great territorial extension of both cities and the marked inequality between areas of interstitial gaps that lack services and the urban areas that are far better equipped¹⁷. In the context of these urban transformations, varied forms of displacement, social practice territorialization, segregation and differentiation of social sectors emerge.

The great spatial changes in Posadas and Encarnación revolve around the Yacyretá hydroelectric dam and the change in its new riverfront. Three observations indicate the convergences and direct the focus of analysis towards these twin cities:

The aspects described above clarify how these two cross-border cities are simultaneously transformed, radically changing and reconfiguring their morphologies, reconstituting their urban fabric and creating new requalification areas. Facing each other, one city seems to be the extension of the other. Along with coastal improvement, new high-quality public spaces have emerged, creating an artificial landscape that would otherwise be missing in these cities. Through urban planning, it becomes evident that these situations represent new opportunities to transform various and unique productive and social activities (^{Brites, 2014}; ²⁰¹⁶).

Changes around the river and the advance of new planning and land-use ordinances have resulted in urban revaluation processes, which, in recent years, have created strong pressure on real estate neighborhoods -or parts of them- including Mboi Ka'ê and Pacu Cua in Encarnación and Chacras, and the settlements located on the west coast and the east coast in Posadas. Social groups characterized by socio-economic vulnerability still reside in these areas. Apart from the fact that many slums have been removed by relocation programs, others have changed through gentrification processes, as is the case with the following old neighborhoods in Posadas: Villa Blosset, la Bajada Vieja, El Brete, etc.

As already shown in other studies (^{Brites, 2016}; ^{Souza & Brites, 2017}), the new forms of displacement imply not only a social/residential substitution of the new spaces but also an economic transformation because they require investments to purchase and rehabilitate depressed areas through the construction of new residential buildings.

Along with aspects relating to the revaluation of the coastal front, it is worth noting that these cities are staging new processes and problems such as those resulting from extending the peri-urban territory, population growth, flow articulation and inter-urban mobility, greater distances, uneven urbanization, peripheralization, spatial dualization, etc. This transformation highlights fragmentation, division and socio-spatial inequalities.

The Table 2 briefly provides the socio-spatial complex processes that characterize Posadas and Encarnación today.

Posadas and Encarnación take advantage of the opportunity structures linked to the border in a complex interplay of competition, articulations and complementarities that transform both cities in an international conurbation. Thus, beyond economic relations (which are asymmetric and changing), the existence of relations between the urban functions of these cities and their inter-urban flows provide them with unique characteristics.

Although commercial activity is of vital importance for city economies, Encarnación is not a monofunctional city or shopping city. The growth of services, the development of a regional university pole, the creation of the Yacyretá infrastructure, and the opening of extensive beaches on the river as well as new spaces for leisure have shifted the focus toward tourism as a productive activity in the regional context. Thus, the economic profile of Encarnación has changed. Recently, the new urban profile of the city has been reflected in the guidelines of the Plan Encarnación Más (2016), which entails land-use planning as well as proposals for a river city, a commercial city and a touristic city, thus recovering the renewed landscape imprint of the new city.

On the other hand, Posadas, whose urban dimensions are nearly triple that of Encarnación, has consolidated its place as a regional urban center, becoming a university city (public-private) and a public administration, service and health center¹⁸. In addition to the infrastructure resulting from the Yacyretá effect, new, high-quality public entertainment spaces have been created, stimulating the development of new real estate developments and new urban capital gains. All these accomplishments result in a more versatile and dynamic urban life in these cities (Figure 6).

Source: Prepared by the authors based on Wikimapia.

Figure 6 Shared urban and socio-spatial processes in Posadas and Encarnación 

Currently, not only has the development of Encarnación’s new coastal front attracted attention, the increase of its infrastructure for tourism, including hotels, recreational complexes, shopping centers, etc., is also worth mentioning. The opening of large beaches on the banks of the Paraná has enshrined Encarnación as the summer city of Paraguay¹⁹, while also making it, along with the waterfront, a meeting space for Posadas and Encarnación inhabitants. Simultaneously, revenues for large-scale events such as the “Carnival” have improved, including the construction of the new “Sambadrome” and a civic center designed to accommodate massive crowds during the summer months. Additionally, regarding tourism, the border and the geographical proximity between cities have begun to be viewed as advantageous features: visitors who arrive in Posadas go to Encarnación and vice versa. This fact allows thinking of new hypotheses concerning an interactive system of competition, opportunities and complementarities between the two cities.

Posadas and Encarnación are “close and linked” cities, with shared urban processes, where socio-spatial and urban changes yield new provisions and social practices, as well as leisure and recreation styles. The availability of an urban transport system creates opportunities to connect Posadas and Encarnación (increase in the flow of people, activities, service consumption, etc.). Moreover, neuralgic areas in these cities, that is, its urban centers, are considerably close. Their urban renewal areas (riverside) are facing each other, and in these spaces, both cities daily prompt new urban and social processes, avant-garde buildings, sport centers, bicycle paths, gastronomic circuits, bars, pubs and nightclubs, bringing life to a series of new urban activities that emerge in parallel.

Conclusions

Posadas and Encarnación share a history of relations in the regional context, traversed by fluid economic interactions and socio-political events, where relational and linking processes have been functioning for a long time. Leaving their specificities aside, both cities share similar socio-urban aspects, and their evolution has entailed the same processes and problems: border flows, Mercosur policies, construction of the international bridge, Border Neighborhood Transit agreements and a most unusual phenomenon, the imprint left in their territories by the Yacyretá coastal treatment.

We argue that the process of complementarity relationships refers to convergent situations, experiences and social practices embedded in border socio-urban issues. Infrastructure, trade, rationalities regarding opportunity structures, mobilities, relational links, shared problems, and the creation of common agendas, among other phenomena, highlight the fact that the development of these cities entail complementary processes of socio-urban articulation.

Despite the restrictive economic regulations and markets of Argentina and Paraguay, both cities -on each side- experience the border locally, engaging in intense business interactions (whether formal or informal, with recreated exchange practices). In this exchange, differential earnings and complementarities create tension and conflict but also foster unity and interaction between these cities. Such tension and competition derive, to a greater extent, from a specific area in the border labor market linked to the commercial sector. This tension is subject to economic circumstances, unstable balances, and processes of differential accumulation and is frequently beyond the control of border policies.

Since these are nearby cities that face each other, the model of twin cities is useful to describe their relationships and address some common features. The movement of people, goods and information, the spaces of flows, the socio-economic processes, and the opportunity structures constitute regular circumstances, which are fused to the physical dimension, where territorial inter-urban and cross-border interaction becomes crucial.

The intense inter-urban articulation is complex and multipurpose, where the commercial, labor, educational, recreational, and familiar aspects play an important role. Although these cities compete and cooperate, today, they share new challenges, such as unequal exchange, extensive territory growth, fragmented urban development, and the need for a better linkage between them. Specifically, this last feature, which focuses on the need for a “faster bridge,” exemplifies the burden of claims and mutual expectations.

Despite the tensions and competition (due to economic asymmetries), the complementary relations between both cities entail potential benefits, according to the differential advantages offered by the border. In addition to having citizens from both urban areas purchasing products and accessing services, the interaction between populations increases and facilitates social, educational and cultural exchanges. Sustained relations and “daily life” improve the mutual understanding between people who share and live the border locally on a daily basis.