History of the Peloponnesian War

The timbers served to hold the bricks together, preventing the structure from becoming weak as it attained height, and they were protected by coverings of skins and hides, so that the workmen and woodwork might be safe and shielded from incendiary arrows.

The wall was mounting to a great height, and the opposing mound was rising with equal speed, when the Plataeans thought of a new expedient. They made an opening in that part of the city wall where the mound came into contact with it, and began to draw the earth in.

But the Peloponnesians became aware of this, and threw into the breach clay packed in reedmats that it might not filter through like the loose earth and be carried away.