Introduction¹

As we have noted in earlier research (^{Tapia & González, 2014}; ^{Tapia & Parella, 2015}), studies on borders have undergone significant changes since the second half of the twentieth century. Moreover, they have become increasingly inter- and transdisciplinary (^{Newman, 2015}). In general, border studies have developed in parallel (^{Zapata-Barrero & Ferrer-Gallardo, 2012, p. 14}) with historic changes including the fall of the Berlin Wall (1989), the consolidation and expansion of the European Union, the terrorist attacks in Europe and the United States, particularly 9/11 (^{Agnew, 2008}), and the recent crisis of Syrian refugees in Europe and the Middle East. All of these events have led to a discussion on borders, their functions, their closing, opening, and containing capability, and the imaginary contents implied in their demarcation. Thus, we have shifted from a few somewhat fixed and separating notions of geopolitical borders from the nineteenth century to optimistic visions of a world without borders in the context of integration processes (the European Union and Mercosur) and, more recently, to border closings and the emergence of fears regarding who crosses and what are their true intentions. Evidently, historical contingencies affect research production on borders; however, not in one case are the results progressive or unidirectional. Frequently, overlapping interpretations or readings that favor one perspective over the other persist.

According to the literature, it is estimated that in the last 20 years, the number of studies on borders have exceeded that of disciplines such as geography, political science, history, sociology, anthropology, and international relations, among others (^{Newman, 2015}). The “crossing” of disciplinary borders is a good metaphor to refer to the cross-disciplinary nature of border studies and to the profusion of publications and entities devoted to this object of study (^{Newman, 2015, p. 14}).² This high productivity has advantages and limitations. The former relates to an increase in case studies of different borders based on ethnographies, surveys, and data exploitation. The limitations arise from the interdisciplinary nature of the debate because the theoretical discussion is complex and there is no “unified scientific subdiscipline” (^{Brunet-Jailly, 2005, p. 634}).

As we have noted, the production on border studies is wide and refers to a series of common notions or glossaries. However, border terminology has been little discussed, including the notions of border, cross-border, or border regions, to note only a few. All of these concepts are used at different scales, from the local to the global, even to refer to different cultural and social categories. Based on the research experience that links border, migration, and mobility, the purpose of this paper is to contribute to the debate on border crossing or transbordering in the context of a region or border area. The aim is to review the production on borders from historical and disciplinary perspectives and to revise the approaches that address cross-bordering from the perspectives of human mobility and cities. The objective is to present an overview of the discussion on borders and the manner in which border crossing intertwines in this debate, with a special focus on population movements around and at the borders. To that end, we review the literature on borders and transbordering, particularly, though not exclusively, the literature analyzing the Latin American experience.

Within the broader debate on borders and transbordering, we focus on analyses centered on territories and on the perspective of those who inhabit the border; otherwise, we run the risk of being misled by broader notions such as transnationalism and globalization. In short, the notion of multiscale or multilevel analysis is used as a heuristic tool to differentiate our project from macro scale or supranational studies, which address globalization. Taking such a positioning does not imply discarding the others; on the contrary, we recognize, as noted by Sassen, the existence of a hierarchy of scales. Simultaneously, however, we agree with the author in that these scales have been and continue to be destabilized. Therefore, it is necessary to recognize that “the global ... simultaneously transcends the exclusive framing of national states yet partly inhabits national territories and institutions” (^{Sassen, 2007, p. 11}).

The article is organized as follows: in the first section, we succinctly review the debate on borders in border studies from a historical perspective as well as the content changes in various disciplines and the ups and downs in the discussion in Latin America. The second part dwells on the theoretical production on border crossing. Consequently, studies that define this notion and apply it to specific cases such as the Euroregions and cross-border regions in Latin America are analyzed. In the third section, we delve into the debate on cross-border metropolises, urban complexes, and conglomerates developed from cases including Mexico-United States, Haiti-Dominican Republic, and Argentina-Bolivia. To conclude, we focus on the link between borders, mobility, and cross-border social practices as a basis for understanding transbordering in border regions.

Borders in Border Studies

Cross-Border Cities, Metropolises and Conglomerates

Another relevant branch for debate relates to the manifestation of border crossing in cities, metropolises, or urban areas located on the borders. It refers to empirical case studies of twin cities that examine the cross-border nature, or lack thereof, in nearby cities. The most prominent cases include cities in Mexico and the United States, and one of the most prolific authors in this sphere has been Tito ^{Alegría (2008)}. Based on studies on Tijuana and San Diego from the 1980s and studies by Hergoz (Herzog as cited in ^{Alegría, 2008}), Alegría analyzes the existence of a cross-border metropolis in this area. To do so, he challenges authors such as Bustamante (quoted in ^{Alegría, 2008}) and contests the claims on the bi-national nature of cities, the existence of the same social structure across borders, and the similarities of economic and social processes on either side of the border (^{Alegría, 2008, p. 131}). Similarly, he criticizes the notion of the cross-border metropolis proposed by Herzog, who states that two aspects must be taken into account to understand border cities: “the first is the process of convergence/integration or divergence/independence of both societies that come together at the border; the second is the possibility and necessity of binationally created policies for border cities” (^{Alegría, 2008, p. 133}). For this author, the border has two antagonistic and unifying roles: the first separates whereas the second unifies border regions. The latter underlie the notion of the cross-border metropolis. In this proposal, Herzog concludes that there is a transnational social system that creates an interest community around the border (^{Alegría, 2007}). Therefore, the interaction promoted by globalization, the network society, and hybridization cause the integration and emergence of a cross-border metropolis, as in the case of Tijuana-San Diego. Thus, the notion of the cross-border metropolis is useful to define other binational pairs of neighboring border cities (^{Alegría, 2008}).

Tito Alegría contests the notion of the binational region and Herzog’s thesis because it does not clearly differentiate between economic space and region. He postulates that the cross-border exchange of goods and services, which gives sense to this region, is not sufficient to define a cross-border region. The author defines a region as an objective social construction, whose content:

Is determined by a set of social, structural, and territorialized relationships. Every relationship has a territorial sphere that includes the location of agents and means directly bound by the relationship as well as the material flows that it embodies (^{Alegría, 2000, p. 95}).

Therefore, to identify an objective region, the phenomenon must be “objectively regionalized, that is, limited in time and space” (^{Alegría, 2000, p. 95}). Consequently, according to Alegría, for the notion of “cross-border continuity” to have a conceptual basis, three theoretical assumptions are required:

i) The social actors of the communities on both sides of the border know similar action procedures. ii) The social actors on both sides of the border interpret and apply the semantic and normative aspects of these action procedures in the same manner. iii) The social actors on both sides of the border have access to the same type of resources. Nonetheless, as indicated by the evidence, such a social structuring is not met at the border (^{Alegría, 2008, p. 137}).

In the case of the Tijuana-San Diego border, Alegría concludes that action procedures on both sides of the border are not similar, that there is no shared knowledge, and, along the same lines, that language is an obstacle for the multiplication of social practices. It is not a matter of sharing practices bounded in time and space but, rather, also sharing a common interpretation of the social practices that “give a sense of social order materialized in meanings. In this manner, meaning construction is intrinsic to shared interpretations, without relying on an external entity” (^{Alegría, 2008, p. 139}). In the case studied, the negotiation of meanings examined by the author on both sides of the border is not frequent; in fact, it is sporadic and focuses on particular aspects of the exchange. With regard to cross-border continuity, Alegría argues that it must exist on both sides of the border, that is, that the conditions that allow the reproduction of the system function equally on both sides of the border. Consequently, the cities studied are “together but not mixed” because they are not integrated in a systemic manner. Therefore:

The hypothesis of a cross-border metropolis implicitly assumes that Tijuana and San Diego represent a systemic unity, that is, that changes in the main activities of one city affect the other. In terms of growth, this means that the drivers and rates of growth in both cities are similar. However, the evidence contradicts this hypothesis (^{Alegría, 2008, p. 143}).

Alegría´s thesis is contested by ^{Dilla (2015)}, who claims that the author's reluctance to accept the existence of cross-border urban systems is based on three assumptions. The notion of system proposed by Alegría is based on a body of theory that he criticizes, namely, “the biological and harmonic formulation underlying the functionalist notion of system” (^{Dilla, 2008a, p. 21}). From this perspective, no urban agglomeration, if its interdependence is left aside, can become a system. Dilla also criticizes the notion of reality described by Alegría, which is presented as an imagined scenario in which “an equitable fusion” is of prime importance (^{Dilla, 2008a, p. 21}) and according to which the interdependencies between cities based on asymmetries are read as a deviation. Finally, he objects to the requirements that Alegría identifies as central to defining transbordering, namely, the interpretation of shared social practices, the existence of common codes, and language. Dilla argues that these requirements are valid for cities within the same national space. Similarly, Brazilian studies on twin cities propose that asymmetries and differences in border areas promote interaction between labor, capital flows, access to resources, and services of collective consumption (^{Machado, 2005}; ^{Marques & Machado, 2008}), among others.

Taking these criticisms as a starting point, Dilla proposes the notion of cross-border urban conglomerates (CUCs) to refer to agglomerations that constitute systems, “but unlike other elaborations, he views them as social constructions based on very contradictory and even conflicting scenarios” (^{Dilla, 2008b, p. 169}). These complexes work in contexts of conflict due to asymmetries and different modes of unequal exchange, which can generate “strong political and cultural tensions” (^{Dilla, 2008a, p. 22}). In this sense, Dilla’s proposal contributes to the debate by including the earnings differentials in binational exchanges and the emergence of distinct subsystems that do not contradict the idea of system formation. However, he warns that for a CUC to exist, at least six conditions must be met, namely: geographical proximity between urban centers, interdependent economic reproduction, the existence of primary relationships (friendship, neighborhood, or kinship), formal and informal shared services, state and social institutional relationships, and a “shared perception of mutual need” (^{Dilla, 2008b, p. 170}). Dilla bases his proposal on the study of border cities in the Dominican Republic and Haiti, where the border separates and connects two asymmetric and unequal sides in economic, institutional, and cultural terms. In his study, he concludes that the notion of the CUC is a new way of viewing the relationship between cities, the pressure on resources, migration, and trade, distinguishing in each case whether the cities analyzed constitute, or not, a CUC.

The debate of studies on border cities deepens the discussion on border crossing while making it more objective. On one hand, similarity parameters, code-sharing, and mutual involvement may constitute cross-border cities or metropolises, as noted by Alegría. However, the most noticeable examples from reality show that inequalities and asymmetries between border cities favor exchange, interaction, and production through mutual dependence, such as in the case in the CUC presented by Dilla. In both cases, we find parameters and dimensions at the meso level (economic relations, agreements, population flows, etc.) to compare or to take into account when defining the cross-border nature of border cities.

Border, Mobility and Territory: Transbordering and Border Practices

As noted above, the notion of the border has experienced changes within the framework of border studies. However, for the purposes of this research, we focus on studies that analyze the intersection between borders and human mobility. As noted above, border studies have ceased to address “layout, demarcation, and location to focus on the practices of border social (re)production, without renouncing the foregoing” (^{Zapata-Barrero & Ferrer-Gallardo, 2012, p. 13}). The tension resulting from human mobility in border crossings is the most noticeable aspect of this relationship. Border closing or hardening -re-bordering- or opening -de-bordering- processes (^{Durand, 2015}) represent the main concerns and tensions that define migration and circulation policies as well as the perception of the role of borders.

In this work, linking border and mobility, from a territorial perspective, answers the search of transbordering in border regions or areas at the local or micro level. We know that from a macro perspective and in the context of globalization, most countries establish bonds with others, with the most obvious being diplomatic and economic relations. At the global level, the highest expression of these links is constituted by the action of “manifestly global organizations such as the ILO (International Labor Organization), global financial markets, the new cosmopolitanism, and international criminal tribunals” (^{Sassen, 2010, p. 22}). However, as noted by Sassen, there are other processes that do not correspond to the global scale as such but, rather, are part of it. These are processes that occur in the territories, in the domain of what we call the national, which, despite its location, is part of globalization. “They are cross-border, multifaceted configurations and networks, which include, in some cases, normative orders and connect subnational or ‘national’ processes, institutions, and actors but not necessarily through the formal interstate system” (^{Sassen, 2010, p. 22}). In some manner, we posit that transbordering would represent a scale of lesser rank that is linked with the national and global spheres but is anchored in a territory. This scale is affected by the interactions that occur around the borders, which, in some cases, are expressions of globalization and, in many others, demonstrations of what is national. In this territorial scale, people are key to explaining the interaction and relationships that occur when crossing the border, using it as means, and, in many cases, making an opportunity out of it. These exchanges are invigorated by the existence of the border, because of it and, sometimes, in spite of it, such that the border, in its territorial expression, acts as a reference for these relationships.

Territory, as a category, has been widely discussed, particularly in recent decades and in the context of globalization. However, in this section, we refer to the debate that relates territory to borders and mobility. In short, we focus on the notion of territory because borders, boundaries, and border-crossing relate to a material or physical space that has controlled the access of people, commodities or goods, and services (^{Haesbaert, 2013, p. 18}). Therefore, what differentiates a territory from an area, space, or place is its direct association with power and control over both resources and people. As Haesbaert states, “simply put, a territory would be a dimension of space where the approach is focused on the relations of power” (^{Haesbaert, 2013, p. 20}); thus, “the territory is not identified and delimited by an external observer willing to study it but, rather, by the social groups that maintain relations of production or reproduction, neighborhood or kinship, etc.” (^{Kralich et al., 2012, p. 114}). Evidently, borders, due to their configuration by national States, have a territorializing feature in terms of defending a sovereign space, becoming a marker of identity and historical memory and a symbol of societal authority and control to act as a filter for people entering and leaving (^{Durand, 2015, p. 312}). However, the desire to attract capital and goods and to participate in the international market requires a redefinition of the regulatory nature of borders that does not always match the free movement of people.

Considering scales is critical to understanding territories, particularly those in the border area because power is unevenly distributed in the territory and it is not the same if border inhabitants, local institutions, or state devices exert such power. This is particularly evident in these spaces because borders materialize territoriality (^{Kralich et al., 2012, p. 115}). Analyzing borders through scales enables the type of power at hand to be examined. From the state perspective and in a traditional sense, “the territory is a macroterritory basically linked to large dominant political-economic structures” (^{Haesbaert, 2013, p. 26}). However, if viewed as a form of resistance that is always present in social relations and warns us of the capacity of agency, then it becomes “microterritories with many other ways of reconstructing power and territory from it” (^{Haesbaert, 2013, p. 26}). Based on this conception of the border, more recent studies in the field of geography pay special attention “to the ways in which social groups identify themselves and express their solidarity through space” (^{Kralich et al., 2012, p. 114}). In this manner, territory is a heuristic category defined on the basis of the cultural and material practices of a society.

The second relevant element for our discussion addresses the agreement presently existing regarding borders as “mainly linked to mobility and not so much to a static, immovable, and non-negotiable reality, based on a physical territorial line” (^{Zapata-Barrero & Ferrer-Gallardo, 2012}). As Benedetti states, borders allow crossing (^{Benedetti & Salizzi, 2011, p. 151}); that is, they make sense inasmuch there is an intention to cross or move across the borderline. In other studies (^{Tapia, 2014}; ^{Tapia & Parella, 2015}), we have noted that the notion of migration is not sufficient to understand the population movements that occur at borders. The bidirectional nature of the concept (origin-destination), the actual establishing in the place of destination, and the length of stay almost always omit a series of movements that, until recently, were classified as migration “ambiguity” (^{Cortes, 2009, p. 38}) or residual migration (^{Mallimaci, 2012}).

Borders are the scenario of a series of movements expressed in daily, weekly, or temporary crosses by individuals who do not intend to establish themselves on the “other side”. Therefore, the notion of mobility allows a better understanding of the movements across or around borders because “it is more comprehensive and includes more aspects than migration” (^{Heyman, 2012, p. 427}). Economic disparities and asymmetries between countries transform borders based on a resource because crossing provides earnings that are not obtained in the national territory or, at least, not in the same proportion. Thus, “borderlines, borders, and mobility become resources to define reproductive strategies that take advantage of the disparities between territories” (^{Benedetti & Salizzi, 2011, p. 151}).

Abelardo Morales coined the notion of cross-border social practices to refer to activities in which crossing the border is a central element. These practices may be adaptive, transformative, productive, or reproductive and generally refer to earning, saving, or reducing the cost of living for border residents who adapt and transform life at the border (^{Morales, 2010}). Similarly, Parella ^{(Parella, 2014)} identifies a number of practices in the Mexicali-Calexico border aimed at taking advantage of living on one side and working on the other, crossing to buy, look after, eat, celebrate, or study (^{Tapia & Parella, 2015}). The literature is full of examples of crosses for consumption, traffic, transhumance, leisure, health, or trade (legal-illegal, formal-informal) purposes in Latin America (^{Aponte, 2012}; ^{Hevilla, 2014}; ^{Jaquet, 2008}; ^{Mallimaci, 2012}; ^{Steiman, 2012}) and in different places (^{Banerjee & Chen, 2013}; ^{Shen, 2014}; ^{Soriano & Fuentes, 2015}; ^{Wang, 2004}) that involve short trips whose aim is to stay for short periods and with a specific purpose related to the place of origin.

As ^{Konrad (2015)} states, the borders are in motion, and theories must be aligned with this “turn” in the social sciences. Movement is strongly related to crossing interaction, flows, relocations, and practices, even in contexts of serious conflicts or disputes. It is necessary to change perspectives to focus on the dynamic interaction that occurs at the border and, in particular, on mobility, instead of focusing on the borderline. As the author claims, the recent production on borders shows that “motion is emerging as a wide field of intellectual inquiry in the social sciences” (^{Konrad, 2015, p. 4}).

A Contribution to the Debate on Border Crossing by Way of Conclusion

Based on this review and on the research experience acquired, we propose that the continuity and stability of border crossing through time, in an enclosed space and based on strategies of life reproduction or productive activities, are at the root of the constitution of a cross-border space or region. From its modern conception, the design of borders was conceived in terms of closure, both to protect and to contain, to prevent undesirable people, property, or goods from crossing. The national character of borders and the design of hardening or opening border policies at different scales are emphasized, with control playing a key role for entry, transit, and exit.

The scientific production on borders, border regions, and cross-border regions or spaces is increasing. Within this development, the concern of different disciplines enriches the analysis and, simultaneously, opens up new theoretical and methodological challenges. On one hand, any study on borders must incorporate several perspectives and disciplines, rendering transdisciplinarity essential to understand what is happening. However, we posit that including national and regional history is key to understanding the context and the changes in the notion of the border in its history. Incorporating long-term analysis makes it possible to understand the resurgence or revival of nationalism and the processes of hardening and closing of borders.

A review of the production on borders presents useful elements to understand what transforms a border region into a cross-border region. On one hand, the proximity of towns or cities is essential but not sufficient. Frequent exchanges and the bidirectional crossings of people constitute explanatory factors of this configuration. Cross-border continuity or the similarities between areas can be a factor to be considered, as in the case of the Euroregions. However, the differences and, above all, the asymmetries are the most important explanatory factors for understanding the increase in crossings or the attempts to do so. The most emblematic cases are the case of the U.S. and Mexican border and, most recently, the external border of the European Union. However, they are not the only cases. At different scales and in different parts of the borders of Latin America, Asia, and Europe, movement and cross-border mobility are recorded through the deployment of productive and reproductive border practices that seek to take advantage of the benefits of crossing. Differences in development often result in exchange rate differences that invite crossing to the other side to work, buy, or access resources that are not available in the country of origin. In this sense, we propose that border crossing is created from below, from the territory, by the people who live in the territory and regularly move across the border, often regardless of bilateral disputes. Different social border practices turn the border into a resource, despite its configuration as a containment space or shelter. Therefore, beyond the entry, stay, or exit restrictions of a national territory in relation to another, people will seek to solve problems or to gain resources by crossing the borderline whenever possible. In doing so, particular territorialities and features, communities, and cities located in the border or around it are reconfigured.

The explanations behind these spaces are varied, as described in the literature, including border consumption, the existence of cross-border labor markets, the development gaps that are expressed in the types of exchanges, all types of services (health, leisure, and education) and licit or illicit, formal and informal activities. Whereas, in the case of Europe, the emergence of cross-border regions has its antecedents in the mid-twentieth century, its expansion became evident by the end of the century. However, its continuity mainly relates to the institutionalized dimension of this bond, formalizing pre-existing territorial links and intense cross-border cooperation. However, configuring the Euroregions would have been difficult without previous interactions, shared interests, or the recognition of mutual dependence, despite the political will behind it.

Thus, we posit that mobility builds the territory by linking border spaces and cities that create transboundaryness or border crossing, at the territorial level, even in spite of the existence of limits and the difficulties sometimes entailed in crossing. However, a methodological challenge emerges, and it entails verifying or validating cross-border regions or border areas. This means that measuring in some manner the magnitude of the exchanges and the manner in which the interaction is constituted is necessary. In addition to analyzing the cross-border practices identified in other studies (^{Tapia, 2014}; ^{Tapia & Parella, 2015}) and the review conducted above, the border crossing nature of a border region must not be taken for granted. This positioning resonates with what ^{Portes, Guarnizo and Landolt (2003)} warned in relation to migrant transnationalism because it is not enough to “invoke some anecdotes” of migrants to speak of transnationalism; establishing some minimum requirements is a must. After reviewing the literature on the subject and on the basis of the research experience, we can state that the continuity of the interactions in time, the magnitude of exchanges involving a number of relevant population in statistical terms, and geographical proximity, whose expression is manifested in mobility through a territory, are three central elements to consider. The explanatory factors may vary because cross-border continuity may be expressed through systemic similarities, as discussed by ^{Alegría (2000)}, or through asymmetries and inequalities on both sides of the border, as stated by ^{Dilla (2008a)}. The links between subnational governments or cross-border cooperation clearly favor interaction, but we argue that they are not necessarily a condition for it.