Battle of the Riachuelo, 1865: the river battle that turned the Paraguayan War

In the War of the Triple Alliance of 1864 to 1870, Paraguay's marshal-president, Francisco Solano López, fought the Empire of Brazil, Argentina and Uruguay. In 1865 his armies invaded northeastern Argentina. To push on south, López needed to clear the Paraná River of the Brazilian and Argentine warships that could cut his supply line along it.²

A squadron built for the sea

The Brazilian navy was slow to answer the Paraguayan offensive, the historian Francisco Doratioto has argued, and a letter written by Admiral Francisco Manoel Barroso on 9 May 1865, discovered and published in 2025 by Pedro Henrique de Souza Ribeiro of the Federal University of Rio de Janeiro, helps explain why. Barroso's ships were built for the open sea, and their draft was too deep for the shallows of the Paraná. In Montevideo he bought a small river steamer, the Eufrásia, which pulled the grounded Argentine steamer Pampeiro and the Brazilian Ivaí and Amazonas off the sandbanks and scouted the channel so that the squadron could move upriver.³

The same fear of shallow water, Ribeiro shows, lay behind Barroso's refusal on 25 May to send two gunboats to Paso de la Patria at the request of the Argentine general Paunero. The letter also asks urgently for flour and biscuit for his men and compares the Paraguayan troops pouring into Brazil to ants, a sign of how the war was being described to justify it.⁴

Ribeiro draws out how improvised the campaign was. Barroso paid for the Eufrásia and for his supplies in Montevideo on his own authority, without any sum voted for the purpose, and the men he had to feed, volunteers and pressed recruits alike, numbered about 2,650. Nothing in the letter suggests that he expected an easy victory; his worries a month before the battle were sandbanks, shallows and food.⁵

The surprise that failed

López's plan was a surprise attack at dawn on the Allied squadron of eleven steamers anchored just south of Corrientes, near the mouth of the Riachuelo, a small tributary of the Paraná. But delays held up Admiral Pedro Ignacio Meza's flotilla, and it did not arrive until 11 a.m.. The surprise was lost.⁶

For the next six hours, according to the Encyclopedia of Latin American History and Culture, the two forces seesawed back and forth across the river. The Paraguayans missed every chance for effective maneuver against the better-armed Brazilian steamers, and the Allies used their superior firepower to good effect.⁷

Barroso's arc

The decisive move came from Barroso himself. He took his flagship, the frigate Amazonas, in a wide arc that let him attack several of Meza's warships one after another. By evening the Paraguayans were retreating upriver. They had lost four of their nine steamers, and the rest were badly damaged.⁸

The Brazilians lost two steamers of their own, the Belmonte and the Jequitinhonha; the Jequitinhonha ran aground, where Paraguayan batteries on the bank destroyed her. Casualties were high on both sides. Meza was wounded and died the next day. Exact numbers of dead and wounded on either side are not given in the sources used here, and estimates in other accounts differ widely.⁹

The war turns

The victory at the Riachuelo denied the Paraguayans any hope of an unchallenged advance south into Argentina. Within weeks López ordered his land forces back into Paraguay, and from then on his campaign was entirely defensive. Barroso was later made Baron of Amazonas, after his flagship, and the novelist Machado de Assis, writing in 1870, presented the battle as the fruit of a just war.¹⁰

Ribeiro cautions against reading the outcome as inevitable. His letter shows a navy struggling with river navigation, supplies and money, with no certainty of final victory a month before the battle. The war that the Riachuelo turned would last five more years and end in 1870 with the death of López and the ruin of Paraguay. Earlier river warfare on the same Paraná, against an Anglo-French squadron, is told in our account of Vuelta de Obligado.¹¹