The boundary separating Haiti and the Dominican Republic stands as a paradigmatic case of the enduring legacies of colonial border-making. Emerging from European rivalries—codified in the Treaty of Ryswick (1697)—a frontier once defined by maroon communities and plantation economies was transformed into a rigid line of imperial sovereignty. Divergent colonial trajectories accentuated this division: French Saint-Domingue emerged in the eighteenth century as the wealthiest sugar colony in the Atlantic world, its prosperity sustained by the labor of enslaved Africans and culminating in the Haitian Revolution. In contrast, Spanish Santo Domingo maintained a more modest and diversified economy—rooted in cattle ranching, subsistence agriculture, and trade—while remaining closely embedded in the institutional and cultural frameworks of Catholic Spain. Independence did little to reduce these structural asymmetries. Haiti’s crushing indemnity to France, its subsequent two-decade occupation of Santo Domingo, and the rise of Dominican authoritarianism—notably Trujillo’s 1937 Parsley Massacre—consolidated antagonism across the island. In the twentieth century, U.S. interventions and bilateral treaties further institutionalized the frontier, often disregarding established patterns of mobility and exchange. Today, stark economic disparities and migration pressures perpetuate tensions, even as cross-border markets and rayano identities underscore the border’s ambivalent function as both a site of exclusion and a space of interdependence.