History of the Peloponnesian War

The wall of the Peloponnesians was built in the following fashion. It had two encircling lines, the inner looking towards Plataea, the outer to guard against attack from the direction of Athens, and the two circuits were distant about sixteen feet from one another.

This interval of sixteen feet had in building been divided up into rooms assigned to the guards; and the whole structure was continuous[*](ie. the two περίβολοι were joined together by a roof.), so as to appear to be a single thick wall furnished with battlements on both sides.