In 1204, the Venetians took this sculpture, which depicts the four joint-rulers of the Roman Empire at the beginning of the fourth century,  from Constantinople as spolia of the Crusade.  The Four Tetrarchs dates to around 300 and is carved of porphyry, a purple-colored marble only quarried in Egypt.  In antiquity, purple implied an imperial or divine association.[1. Charles Freeman, The Horses of Saint Mark’s, (New York: The Overlook Press, 2004), 88.] To the Venetians, taking this sculpture from its original location in the Byzantine Capital symbolized that the four tetrarchs who once ruled the lands of the present-day Byzantine Empire, became the conquered tetrarchs and that Venice became one of the dominant powers in their stead.[2. Domenico Crivellari and Maria Da Villa Urbani, “Section Dedicated to Stone and Marble,” Basilica Di San Marco, http://www.basilicasanmarco.it/WAI/eng/basilica/architettura/interne/pietre_marmi.bsm
(accessed November 11 2011)]