In this study, we offer a relational approach to theorizing boundaries for the Maya, adapting Mills’ (2018) concept of “boundary objects” as a means of understanding how people and things bridge or cross boundaries and were critical for developing and maintaining allied relations. We trace a network of sites on both sides of the Guatemala–Belize border dating to the Terminal Classic and Postclassic, which are generally characterized as times of increased conflict, movement and migration of people, and disruption in dynastic succession with an emphasis on shared governance. We examine the introduction of northern-style traits in the eastern Maya lowlands during the Terminal Classic and Postclassic periods, including circular and colonnaded buildings and distinctive portable goods such as molded-carved ceramics, phallic and turtle effigies, and other material forms. We suggest that during fractious periods in Maya history, northern traits were implicated in boundary crossing negotiations and entangled relations, which included marriage alliances with “foreigners” as a means of elite legitimation.