After the fall of the Humaitá fortress in July 1868, Francisco Solano López centered his troops in a strong position at the Pikysyry stream, which runs on the left margin of the Paraguay River.
To circumvent it, Caxias decided to build an 11-kilometer-long road on the right bank of the Paraguay River, passing through the Gran Chaco swamps, and leading to the Paraguayan rear.
With the aid of the Brazilian Imperial Navy, Caxias carried 23,000 troops to the beginning of the road, from where they advanced along the right river bank, outflanking the enemy's fortified position.
The Navy ships, after reaching Angostura pass, sailed north, where they re-embarked the troops from the road and carried them to the left bank in San Antonio, north of the enemy position.
Solano López, believing that the allied troops could not cross Chaco, was caught by surprise when the allied troops assaulted his rear, being forced to retreat with his surviving troops. This led to the battles of Itororó, Avaí and Lomas Valentinas.