History of the Peloponnesian War

And at every tenth battlement there were high towers of the same width as the wall, extending both to the inner and outer faces of it, so that there was no passage left at the sides of the towers, but the guards had to go through the middle of them.

Now at night when the weather was rainy the guards left the battlements and kept watch from the towers, which were not far apart and were roofed overhead. Such, then, was the wall by which the Plataeans were beleaguered.