Square surrounded by colonnades, in which were placed the offices of the various collegia or guilds of boatmen, raftmen and others, which had a special importance at Ostia; the names of the guilds may still be read in inscriptions in the mosaic pavements of the chambers.
The style is commonly called Byzantine; but some of the most striking features of the churches of Ravenna - the colonnades, the mosaics, perhaps the cupolas - are not so much Byzantine as representative of early Christian art generally.
This gives access to a whole series of halls and private rooms (halls " of the Colonnades," " of the Double Axes," " Queen's Megaron" with bath-room attached and remains of the fish fresco, " Treasury " with ivory figures and other objects of art), together with extensive remains of an upper storey.
The facades presented continuous colonnades on each floor with semicircular high stilted arches, leaving a very small amount of wall space.
It consists of two storeys with open colonnades, forming a long loggia on the ground and first floors, with seventeen arches on the sea front and eighteen on the other facade.