modern wall circuit largely matches the ancient and
original lower rows belonging to the first boundary
wall measuring up to 14 feet in height and consisting
of large superimposed stone-blocks laid in regular ashlar
courses to form portions of up to nine overlapping rows.
The overall shape is that of rectangle having a perimeter
of about 2 miles. Only in the south-east the modern
circuit veers off the original Etruscan circuit although
surveys carried out in 1929 by the Archaeological Superintendency
confirmed the presence in this portion of ancient walls
extending well beyond the later medieval wall circuit
built in the first half of the 13th century. No trace
was left of the original gates with the exception of
the Porta Bifora although one may suppose they possibly
matched the later medieval gates. The original boundary
walls date back to the late 4th century B.C.