That of the limestone atriums (outer walls of the houses of ashlar-work of Sarno limestone, inner walls with framework of limestone blocks, filled in with small pieces of limestone).
Grey tufa period; ashlar masonry of tufa, coated with fine white stucco; rubble work of lava.
Of the best rubble masonry, an ashlar floor of blocks of close-grained trachyte being laid directly under the bridge, where the action was severest.
The design of these entrance gateways is extremely simple and massive, depending for their effect on the fine ashlar masonry in which they are built, the decoration being more or less confined to ornamental disks.
The simple plain ashlar masonry still predominates, but the wall surface is broken up with sunk panels, sometimes with geometrical patterns in them.