The Patriarchal Cathedral Basilica of Saint Mark , commonly known as St Mark's Basilica , is the cathedral of the Patriarchate of Venice; it became the episcopal seat of the Patriarch of Venice in 1807, replacing the earlier cathedral of San Pietro di Castello. It is dedicated to and holds the relics of Saint Mark the Evangelist, the patron saint of the city.

The church is located on the eastern end of Saint Mark's Square, the former political and religious center of the Republic of Venice, and is attached to the Doge's Palace. Prior to the fall of the republic in 1797, it was the chapel of the Doge and was subject to his jurisdiction, with the concurrence of the procurators of Saint Mark for administrative and financial affairs.