church in Venice that was begun in its original form in 829 (consecrated in 832) as an ecclesiastical structure to house and honour the remains of St. Mark (Mark, Saint) that had been brought from Alexandria. St. Mark thereupon replaced St. Theodore as the patron saint of Venice, and his attribute of a winged lion later became the official symbol of the Venetian Republic. San Marco Basilica, built beside the Palazzo Ducale, or Doges' Palace, also served as the doge's chapel. It did not become the cathedral church of Venice until 1807.

The first basilica was burned in 976 during a popular revolt against the doge Pietro Candiano IV but was restored under his successor, Doge Domenico Contarini (died about 1070); the present basilica was completed in 1071. The plan is a Greek cross, and the building is surmounted by five domes. The design is distinctly Byzantine, and it is likely that both Byzantine and Italian architects and craftsmen were employed in the construction and decoration. Over the centuries, additions of sculpture, mosaics, and ceremonial objects have increased the church's richness. The famed four bronze horses on the west facade gallery, for example, were brought to Venice at the time of the Fourth Crusade (1204) from Constantinople, where they had been part of a Greco-Roman triumphal quadriga (a sculpture of a chariot drawn by four horses abreast). Though originally placed in the Arsenal, they were set up in the mid-13th century on the exterior of San Marco. They were removed to Paris by Napoleon (Napoleon I) but were returned in 1815. Later, to protect them from damage, the originals were brought inside and replicas were put in their place.

The basilica's interior is decorated throughout with mosaics on gold ground and with many varieties of marble; the floor is of inlaid marble and glass. In the restricted light their colours glow. The screen separating the choir from the nave has marble statues, masterpieces of Venetian Gothic sculpture by Jacobello and Pier Paolo dalle Masegne.