When the Roman Emperor Diocletian divided his huge Empire into two, he created two Emperors, and four Caesars, in what it was called the Imperial Tetrarchy (from tetra, 4 in Greek).
This statue, a fine example of Byzantine Art, was in Constantinople, also called Byzantium. It was robbed during the tremendous 4th Crusade, that sacked the city and precipitated its doom, together with many riches and works of Art, such as the horses now on top of St. Mark's Cathedral, here in Venice...