The Plaza General San Martín is the main green space in the Retiro neighborhood of Buenos Aires. Inaugurated in 1862, where there used to be a bullring, it was declared a National Historic Site in 1942.

The square is bounded by Santa Fe Avenue and the streets Esmeralda, Arenales, Maipú, Avenida del Libertador, Florida and San Martín.

A bronze plaque near Santa Fe Avenue describes its history, recalling its past as the Retiro neighborhood and Plaza de Toros, and its military use during the defense of Buenos Aires in the second English invasion. It also mentions that it was the place where General San Martín formed the Regimiento de Granaderos a Caballo.

In the colonial period, one version of history states that in 1537 a soldier named Sebastián Gómez committed the first crime in Buenos Aires, repenting and building a hermitage with a cross in the ravine. This cross, known as "Cruz Grande", was present when Juan de Garay arrived in 1580. In 1692, Governor Agustín de Robles built a rest house in El Retiro, which later became known as the "Quinta de Riglos" and was later sold to the "South Sea Company", which used it for the slave trade.

In 1800, a bullring was built in El Retiro, which was the scene of clashes during the English invasions of 1806 and 1807. In 1812, the grounds of the plaza were occupied by the barracks where General San Martín organized the Regimiento de Granaderos a Caballo. Bullfighting was prohibited in 1822, and the remains of the bullring were used to build an artillery barracks in 1823.

In 1856, the Retiro area was developed with the construction of a gas depot and the beginning of the horse railroad between Retiro and Belgrano. In 1862, the equestrian statue of San Martín was inaugurated, and in 1874, the landscaper Eugene Courtois completely remodeled the square.

Plaza San Martín became a sought-after area after the yellow fever epidemic of 1871, with the Porteño upper class building residences around it. In 1909, the Primitive Gas Company gave land for the expansion of the square, which was redesigned by Charles Thays and his son Carlos Leon Thays.

Among the monuments and sculptures in the square are the Monument to General San Martín and the Armies of Independence, the Monument to the Fallen in Malvinas, and "La duda" by the French artist Cordier.

The square has also been the scene of cultural events, such as the exhibition "Culture for Peace, United Buddy Bears" in 2009 and the "Tower of Babel" by Marta Minujín in 2011.

The current design of the plaza is the work of architect and landscape architect Carlos León Thays, son of the famous French landscape architect Carlos Thays. The square is home to a great variety of botanical species, and is divided into two sectors: a grassy ravine from where the Monumental Tower can be seen, and a flat area surrounded by groves of trees and historic buildings such as the Kavanagh and the Palacio Paz.