Paso de Patria is the country's southern tip, near the confluence of the Paraguay and Paraná rivers, across from the Argentine town of the same name. It is a small, peaceful town frequented by anglers after dorado and surubí. To the west stretch wetlands with capybaras, marsh deer, caimans and birds; toward the Paraná, sand dunes appear. The Allied invasion of Paraguayan territory began here in 1866, and the landscape still carries that weight.

Founded on 24 July 1847, it was fortified by Francisco Solano López, who set up his headquarters there in November 1865. In April 1866 the Allied armies crossed the Paraná in this area, and the fighting moved to the nearby marshes, such as Estero Bellaco and Tuyutí, in May of that year, among the bloodiest battles of the war.