An earlier version of the present Basilica was built on this site in 829, when Venetian merchants acquired the relics of St. Mark at Alexandria. In the 11th century it was remodelled in imitation of the Basilica of the Apostles at Constantinople. It has served as the city's Cathedral since the 12th century. The succeeding centuries, especially the fourteenth, all contributed to its adornment, and seldom did a Venetian vessel return from the Orient without bringing a column, capitals, or friezes, taken from some ancient building, to add to the fabric of the basilica. Its whole pavement is mosaic; it contains gold, bronze, and the greatest variety of stones. The fašade is decorated with mosaics of different periods, Byzantine sculptures, and statues of the Evangelists and the Saviour. The four horses of gilded bronze above the great doorway date to Classical Antiquity; by some accounts they once adorned the Arch of Trajan. The horses were long displayed at the Hippodrome in Constantinople, and in 1204 Enrico Dandolo brought them to Venice as part of the loot sacked from Constantinople from in the Fourth Crusade. The mosaics of the atrium and the interior belong partly to the tenth century. The plan of the interior consists of three longitudinal and three transverse naves. Over the high altar is a baldacchino on columns decorated with eleventh-century reliefs; the altarpiece is the famous Pala d'oro (Golden Pall), Byzantine metal-work of the year 1105, originally designed for an antependium. Behind the high altar is another altar with alabaster columns. The choir stalls are embellished with inlaying by Fra Sebastiano Schiavone, and above them on both sides are three reliefs by Sansovino. On the two marble pulpits of the ambo are statuettes by the Massegne brothers (1394). Also in the choir are Sansovino's bronze statutes of the Evangelists and Caliari's of the Four Doctors. The crypt is underneath the choir.