The stone grates located beneath the arch of the Porta San’ Alippio are Islamic emulations of stone carving found throughout the Middle East.  The three grates occupy rounded, arch-shaped openings above the portal and beneath the ogee arch.  These grates are thin slabs of stone carved into delicate, interlocking, geometric patterns.  These interlacing geometric patterns are commonly found throughout Islamic art and across a variety of different architectural media in the Middle East such as brick work, marble inlay and facing, mosaics, ceramics, tiles, and wood carving, and Venetian merchants would have seen ornamental, geometric patterns like those found in the stone grates on San Marco throughout the Islamic world while on their trade routes.[1. Dominique Clevenot, Splendors of Islam: Architecture, Decoration and Design. (New York: The Vendome Press, 200) 143.]

The direct Islamic precedent for these stone grates is the Great Mosque at Damascus, a stop on some trade routes of Venetian merchants.  The stone grates at Damascus were located over small window openings around the mosque as well as above the main entrance into the mosque.  The emulation of the window grates from Damascus symbolized the economic power of Venice as the result of their mercantile relations in the Middle East.