The Battle of Curupayty was a key battle in the Paraguayan War. On the morning of September 22, 1866, the joint force of the Imperial (Brazilian), Argentine and Uruguayan armies attacked Paraguayan fortified trenches on Curupaity. The Paraguayans were led by General José E. Díaz. This position was held by 5,000 men and 49 cannons, some of them in hidden places out of the attackers view.