That potentate commenced the erection of walls, twenty-one miles in circumference, which were finally completed in the reign of Probus (A.D.

276), were restored by Belisarius (A.D.

537), and are to be seen in detached portions, in the fortifications of the modern city, to the present day.
At the date of our story, then (A.D.

408), the walls remained precisely as they had been constructed in the reigns of Aurelian and Probus.
They were for the most part made of brick; and in a few places, probably, a sort of soft sandstone might have been added to the pervading material.

At several points in their circumference, and particularly in the part behind the Pincian Hill, these walls were built in arches, forming deep recesses, and occasionally disposed in double rows.