Both it and the arch are built of Istrian stone.
As to the roads leading out of Italy, from Aquileia roads diverged northward into Raetia, eastward to Noricum and Pannonia, and southwards to the Istrian and Dalmatian coasts.
The delicate creamy Istrian stone, which is now so prominent a feature in Venetian architecture, did not come into common use till after the 11th century, when the Istrian coast became permanently Venetian.
The whole surface of the ponderous upper storey is covered with a diaper pattern in slabs of creamy white Istrian stone and red Verona marble, giving a delicate rosy-orange hue to the building.
The Istrian stone of which the edifice is built has taken a fine patina, which makes the whole look like some richly embossed casket in oxidized silver.