Admiral Tamandaré personally commands the Brazilian naval forces in the blockade of Paysandú that begins on December 3, 1864 with one corvette and four gunboats.
The city is garrisoned by twelve hundred and seventy-four men with fifteen cannons under the command of Colonel Leandro Gómez.
Flores besieges it by land with eight hundred infantrymen and seven cannons and receives on December 4 the support of five hundred and sixty Brazilian troops.
Tamandaré sends a message to Gómez to surrender and avoid unnecessary bloodshed.
The Brazilian envoy, however, is repelled by shots fired under the order of Gómez.
Despite several attacks, the Brazilian and Colorado forces are incapable of taking the city.
Tamandaré opts to wait for the Brazilian army that had entered Uruguayan territory in December 1.
Aguirre sends the Argentine general Juan Sáa with two thousand men to help the besieged forces, forcing the Brazilians to briefly lift the siege and depart to face the new threat.
Sáa, giving up his objective, retreats to the other side of the Rio Negro.
The Brazilian army that had invaded Uruguay with six thousand men and twelve cannons is commanded by Field Marshal João Propício Mena Barreto, the Baron of São Gabriel.
It is followed by twelve hundred militia cavalrymen at the service of the tatter Antônio de Sousa Neto.
On December 29, Mena Barreto camps next to Paysandú with two infantry brigades and an artillery regiment, raising the Brazilian forces to twentt-two hundred and ten men.
The cavalry commanded by Brigadier General Manuel Luis Osório (later Marquis of Erval) remains some kilometers away to protect the besiegers from any unsuspected attack.
Gómez executes a young Brazilian sailor who had been taken prisoner and puts his head in a pole, infuriating the Brazilian troops.
On December 31, the Brazilians and Colorados renew the assault.
