History of the Peloponnesian War

The timbers served as a frame for them, to prevent the building from being weak as it became high; and for curtains it had skins and hides, so that the workmen and the timbers were not exposed to fiery missiles, but were in safety.

So the wall was raised to a great height, and the mound rose opposite to it no less quickly. The Plataeans also adopted some such device as follows: they took down a part of the wall, where the mound lay against it, and carried the earth into the city.

The Peloponnesians, on perceiving this, rammed down clay in wattles of reed, and threw it into the breach, that it might not be loose, and so carried away like the soil.

Being thus baffled, the Plataeans ceased from this attempt; but having dug a passage under ground from the city, and having guessed their way under the mound, they began again to carry the soil in to them. And for a long time they escaped the observation of the enemy outside; so that though they continued to throw on materials, they were further from finishing it; as their mound was carried away from beneath, and continually sinking down into the vacuum.