It is chiefly remarkable for its finely preserved fortifications. The external walls, which have a circuit of about 3 km, are constructed of polygonal masonry; the blocks are carefully jointed, and the faces smoothed. With our present knowledge of such constructions their date cannot certainly be determined. They are not preserved to any very considerable height; but the arrangement of the gates is clearly traceable; as a rule they come at the end of a long, straight stretch of wall, and are placed so as to leave the right side of any attacking force exposed. On the north there is, for a length of about 150 m, a triple line of defences of later date (possibly added by the Roman colonists), inasmuch as both the city wall proper, and the double wall thrown out in front of it are partly constructed of concrete, and faced with finer polygonal masonry (in which horizontal joints seem to be purposely avoided).[3]
