C. Julius Caesar, Gallic War

It was necessary, at one and the same time, to procure timber [for the rampart], lay in supplies of corn, and raise also extensive fortifications, and the available troops were in consequence of this reduced in number, since they used to advance to some distance from the camp, and sometimes the Gauls endeavored to attack our works, and to make a sally from the town by several gates and in great force. Caesar thought that further additions should be made to these works, in order that the fortifications might be defensible by a small number of soldiers. Having, therefore, cut down the trunks of trees or very thick branches, and having stripped their tops of the bark, and sharpened them into a point, he drew a continued trench every where five feet deep. These stakes being sunk into this trench, and fastened firmly at the bottom, to prevent the possibility of their being torn up, had their branches only projecting from the ground. There were five rows in connection with, and intersecting each other; and whoever entered within them were likely to impale themselves on very sharp stakes. The soldiers called these "cippi." Before these, which were arranged in oblique rows in the form of a quincunx, pits three feet deep were dug, which gradually diminished in depth to the bottom. In these pits tapering stakes, of the thickness of a man's thigh; sharpened at the top and hardened in the fire, were sunk in such a manner as to project from the ground not more than four inches; at the same time for the purpose of giving them strength and stability, they were each filled with trampled clay to the height of one foot from the bottom: the rest of the pit was covered over with osiers and twigs, to conceal the deceit. Eight rows of this kind were dug, and were three feet distant from each other. They called this a lily from its resemblance to that flower. Stakes a foot long, with iron hooks attached to them, were entirely sunk in the ground before these, and were planted in every place at small intervals; these they called spurs.