The Cathedral of San Ciriaco, also known as the Cathedral of Ancona, is a Roman Catholic cathedral located in the city of Ancona, Italy. Dedicated to Saint Ciriaco, the cathedral dates back to the 11th century, although it underwent several modifications and restorations throughout the centuries.

The cathedral is situated on a hill, overlooking the sea and the port of Ancona. Its architecture is a mix of different styles, reflecting the various historical periods in which it was built and renovated. The façade, for instance, features a Romanesque portal, a Gothic rose window, and a Renaissance-style loggia.

The interior of the cathedral is equally impressive, with its nave and side aisles lined with chapels, altars, and frescoes. Some of the most notable works of art housed in the cathedral include the frescoes of the life of Saint Ciriaco by Girolamo da Camerino, the bronze statue of the saint by Girolamo Lombardo, and the beautiful 13th-century mosaic floor depicting the months of the year.

The cathedral is also home to several relics, including the mummified remains of Saint Judas Cyriacus, a disciple of Jesus who was martyred in the 1st century AD, and a fragment of the True Cross.