First Battle of Tuyutí The First Battle of Tuyutí was a Paraguayan offensive in the Paraguayan War . The allied victory added to the Paraguayan troubles that began with a failed offensive and continued with the loss of its fleet in the Battle of Riachuelo . In early May 1866 , a Paraguayan attack at a marsh called Estero Bellaco failed . As the allies camped for over two weeks before resuming their advance , Paraguayan leader Francisco Solano López ordered a May 24 surprise attack on Tuyutí , a " a swampy , scrub - brush savannah " . The Paraguayans attacked in three columns , and soon the battle turned into " a series of charges and countercharges , a Latin American version of Waterloo " . The Paraguayan columns continued to attack , but never could overcome the allied firepower . Tuyutí was the last major Paraguayan attack . Ultimately , it was a devastating Paraguayan defeat : of the 6 , 000 men wounded after the battle , a large percentage would die subsequently . The Paraguayan military was decimated . The May 24 , 1866 battle of Tuyutí is known as the First Battle of Tuyutí ; the second battle occurred on November 7 , 1867 , and was an indecisive and less consequential battle in which each side lost about 2 , 400 men . Battle description . From a small hill , with President Lopéz himself commanding the troops , the Paraguayans prepared for a decisive battle . Twenty - four thousand Paraguayans , hoping for the destruction of the allied forces , attacked at midday on May 24 after a rocket announced the order , and the battle began . Lopéz tried to circle the allies with two strong wings as his center forced them to hold positions . His left faced the Argentines , while the Uruguayans were in the center with the Brazilians and engaged the right wing . The terrain was not suitable for movement . The attack began in the center , where the Uruguayans were forced back by surprise with some Brazilian Volunteer Battalions . On the left of the allied encampment , Captain Emilio Mallet had ordered the construction of a large moat in front of his artillery pieces . When the Paraguayan onslaught reached it , they were in grapeshot range and unable to cross the obstacle . The Paraguayans tried to circle the artillery , avoiding the incoming fire , but encountered Antonio Sampaio ' s 3rd Infantry Division . This unit fought desperately in the muddy terrain with its commander dying in the process , having fought stubbornly . At this point , Osório ordered his reserves to attack and repelled the Paraguayan center . On the allied left , the Paraguayans forced back the few Brazilian units , almost reaching the Allied camp . Osório reinforced the Brazilian lines with various units , finally committing the 2nd Cavalry Division , commanded by General Mena Barreto . The Paraguayans continued to attack until they were encircled and annihilated . In the Argentine sector , the Paraguayan cavalry routed the dismounted Argentine cavalry that faced them . Soon , the Argentines had to engage all of their units and even then barely held the enemy . The Paraguayans fled , losing about 12 , 000 or 13 , 000 men , while the allies took about 4 , 000 or 5 , 500 casualties , mostly wounded . The largest battle ever fought in South America had just ended . Lopéz ' s flanking maneuver had failed , but it had been very close to succeeding . In fact , the Allies were unable to pursue the enemy due to the few horses they had remaining . They needed to regain strength and rebuild .