The Battle of Estero Bellaco was one of the bloodiest battles of the Paraguayan War (1865–1870), with the Republic of Argentina, the Empire of Brazil and the Oriental Republic of Uruguay banded together against the Paraguayan government of Marshal Francisco Solano López. This battle took place on May 2, 1866. The Paraguayan army lost 2000 men and 300 were taken prisoner by the troops of Argentina, Brazil and Uruguay.