History of the Peloponnesian War

As for the wall of the Peloponnesians, it was thus built. It consisted of a double circle, one towards Plataea and another outward in case of an assault from Athens. These two walls were distant one from the other about sixteen foot;

and that sixteen foot of space which was betwixt them was disposed and built into cabins for the watchmen, which was so joined and continued one to another that the whole appeared to be one thick wall with battlements on either side.

At every ten battlements stood a great tower of a just breadth to comprehend both walls and reach from the outmost to the inmost front of the whole, so that there was no passage by the side of a tower but through the midst of it.

And such nights as there happened any storm of rain, they used to quit the battlements of the wall and to watch under the towers, as being not far asunder and covered beside overhead. Such was the form of the wall wherein the Peloponnesians kept their watch.