Battle of Estero Bellaco 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 . The Battle . The April 16 , 1866 Brazilian troops crossed the river under Marshal Osorio and settled at Fort Itapirú . Then the same day , General Flores crossed in front of the First Army Corps Argentina and Uruguay infantry division . The next day did Paunero troops . General Flores , positioned in Estero Bellaco , was attacked on May 2 by a force of 6000 men Paraguayan four pieces of artillery . The Paraguayans almost overwhelmed the Argentine troops , in complete confusion until they were aided by twelve legions of booking . On May 2 , 1866 , Marshal Lopez ordered an offensive reconnaissance south of Estero Bellaco , to prevail the location of the opponent . Allied forces entered Paraguayan countryside . The enemy army retreated without resistance . All predicted next successful and secure . Following in the footsteps of troops Lopez , moved by the royal road Humaitd , until , without difficulty , the South Bellaco Estero , camped near which the vanguard , consisting of four battalions Uruguayans , Brazilians four battalions , four pieces of artillery Some regiments of cavalry and two hundred riders riograndense the particular escort General Flores . In all , seven thousand men of the three weapons . The position of Flores forces was as follows , at the time : The Brazilians cited four battalions were encamped behind a smooth blade . The 7th Battalion , which was the most advanced , protected the four pieces of artillery , 1 regiment . A half mile to the rear were the 21 and 38 bodies " Fatherland Volunteers " . The Uruguayan battalions April Twenty , Florida , Independence and Freedom occupied the left of the imperial troops . At noon , when the Allies were given to devour the ranch , the Paraguayans did burst through the three steps of Estero , sweeping the outposts of the vanguard . The Paraguayan cavalry thrust planted at first the confusion between Brazilian forces and oriental again remade battalions and regiments and received timely reinforcements , was rejected along with the bodies of infantry engaged in the operation . Indeed , when the vanguard of the allied army had been defeated , Colonel José Hedwig Diaz , commander of the Paraguayan troops , wanted to go further still . Instead of ordering the withdrawal immediately , since the aim of the operation had been completed , were engaged in a reckless pursuit , to crash into the bulk of the Allied army . And had to withstand the pressure of all the power of the moving opponent . Across the Estero , Diaz scuppered a bypassing of the Brazilian troops , tried by Step Cider , twice rejecting the bayonet , forcing them to flee . Location of Estero Bellaco . This estuary is located in the Ñeembucú Department , Paraguay , bordering the river of the same name .