"The Horses of Saint Mark were installed on the basilica in about 1254. They date to Classical Antiquity; by some accounts they once adorned the Arch of Trajan. The horses were long displayed at the Hippodrome of Constantinople, and in 1204 Doge Enrico Dandolo sent them back to Venice as part of the loot sacked from Constantinople in the Fourth Crusade.
" They were brought to Paris by Napoleon in 1797 but returned to Venice in 1815. After a long restoration, since the 1990s they have been kept in St Mark’s Museum (inside the basilica). The horses now on the facade of the cathedral are bronze replicas." - Wikipedia: St Mark's Basilica