The Venetians brought back columns from Constantinople as spolia of the Fourth Crusade and placed them  around the five arched portals of the West facade of San Marco.  By placing the multi-colored columns near the arched portals, the Venetians created their own interpretations of triumphal arches on the facade.  These triumphal arches, like those of antiquity, symbolized to the Venetians the commemoration of their victory over the Byzantine Empire, and their inheritance of the Empire’s  trading ports and land.  Additionally, the color of the columns also held symbolic meaning for the Venetians.  The red-purple porphyry columns symbolized imperial status, and represented the Venetian power in the lands of the fallen Byzantine Empire.  The green, black, and white marbles symbolized the original religious function of San Marco.   The columns placed on the facade of San Marco therefore reminded the viewer of the original, religious function of San Marco and simulataneously symbolized the new, powerful and victorious identity of Venice within the Latin Empire.[1. 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 11 November 2011).]