The Battle of San Lorenzo was fought on February 3, 1813 in San Lorenzo, Argentina, then part of the United Provinces of the Río de la Plata. A Spanish Royalist army under the command of Antonio Zabala was defeated by the Regiment of Mounted Grenadiers, under the command of José de San Martín. This battle was the baptism of fire for this military unit, and for San Martín in the Spanish American wars of independence.
Montevideo, a royalist stronghold during the Argentine War of Independence, was under siege by José Gervasio Artigas. The city raided population centres along the nearby rivers for supplies. José de San Martín, who shortly before had arrived in Buenos Aires and formed the regiment, followed the royalist ships to San Lorenzo. The area around San Lorenzo formed a large empty plain, the regiment hid inside the San Carlos convent during the night and San Martín studied the battlefield and the enemy ships from the tower. The battle started at the dawn whereupon the grenadiers made a surprise pincer movement to trap the enemy forces. One column was led by San Martín, and the other by Justo Germán Bermúdez. The Royalists were led by Antonio Zabala. San Martín fell from his horse, and was nearly killed, but Juan Bautista Cabral and Juan Bautista Baigorria intervened and saved him. The royalists were defeated, but kept raiding villages for some more time afterwards.