San Martín moved the regiment from Retiro to Rosario, nearing the river at San Pedro and San Nicolás. He was following the Spanish ships and moved at night to avoid detection. San Martín had one hundred and twenty men for this action, reinforced at Rosario by a militia of seventy men under the command of Celedonio Escalada. Those reinforcements included twenty-two rifleman, thirty cavalry, a small cannon and men armed with knives. Escalada had made other actions against the royalists before this battle. San Martín discovered that the royalists intended to pillage the San Carlos Convent and pressed the march to arrive there first. One-hundred royalists landed on San Lorenzo, but the only food available to them was some chickens and watermelons. Aware of the risk of pillage, the population had removed the cattle from the area before the royalists arrived. Escalada arrived in San Lorenzo before the bulk of the patriot army, but the dust trail from the path to Rosario revealed their presence. Escalada attacked them but their ship had a longer range than his cannon, keeping him at bay. He was forced to retire when he found a Paraguayan prisoner who had escaped from the ship. The Paraguayan disclosed the size of the royalist army and their plan of attacking the convent with a larger force, suspecting that the local money was kept in it. They did not attack the convent right away, requiring time to prepare the two field cannons. Escalada returned with San Martín and relayed the news. The march from Retiro to the convent took only five days, thanks to the cadet Ángel Pacheco. Pacheco moved ahead of the regiment and prepared horses in advance at the relay positions. The whole army arrived on scene during the night of 2 February and hid inside the convent. They entered through the rear door and were not allowed to light fires or speak during the night. San Martín studied the enemy and the battlefield from the convent's tower, using a monocular.