This kind of circumvallation, which the Greeks called ἀποτειχισμός and περιτειχισμός, was employed by the Peloponnesians in the siege of Plataea (Thucyd. ii.78, iii.20‑23). Their lines consisted of two walls (apparently of turf) at the distance of 16 feet, which surrounded the city in the form of a circle. Between the walls were the huts of the besiegers. The walls had battlements (ἐπάλξεις), and at every ten battlements was a tower, filling up by its depth the whole space between the walls. There was a passage for the besiegers through the middle of each tower. On the outside of each wall was a ditch (τάφρος). This description would almost exactly answer for the Roman mode of circumvallation, of which some of the best examples are that of Carthage in modern-day Tunisia by Scipio (Appian, Punic. 119, &amp;c.), that of Numantia in modern-day Spain by Scipio (Appian, Hispan. 90), and that of Alesia in modern-day France by Caesar (Bell. Gall. vii.72, 73). The towers in such lines were similar to those used in attacking fortified places, but not so high, and of course not moveable. (Lipsius, de Milit. Rom. v.5, in Oper. iii. pp156, 157; Poliorc. ii.1, in Oper. iii.283).