St. Mark's Basilica
The basilica on Piazza San Marco was built to house the relics of St. Mark the Evangelist and rebuilt in its current Byzantine form in the 11th century, its exterior and domes covered in mosaics accumulated over eight centuries. Inside, gold-ground mosaics cover roughly 8,000 square metres of ceiling and upper walls, telling biblical scenes in a style that owes as much to Constantinople as to Italy. The nave itself is free to enter, but the real draws are the separate paid sections: the Pala d'Oro altarpiece behind the high altar and the treasury of loot brought back from the Fourth Crusade.