Gallic War (7.71-7.74)

Vercingetorix adopts the design of sending away all his cavalry by night, before the fortifications should be completed by the Romans. He charges them when departing "that each of them should go to his respective state, and press for the war all who were old enough to bear arms; he states his own merits, and conjures them to consider his safety, and not surrender him who had deserved so well of the general freedom, to the enemy for torture; he points out to them that, if they should be remiss, eighty thousand chosen men would perish with him; that upon making a calculation, he had barely corn for thirty days, but could hold out a little longer by economy." After giving these instructions he silently dismisses the cavalry in the second watch, [on that side] where our works were not completed; he orders all the corn to be brought to himself; he ordains capital punishment to such as should not obey; he distributes among them, man by man, the cattle, great quantities of which had been driven there by the Mandubii; he began to measure out the corn sparingly, and by little and little; he receives into the town all the forces which he had posted in front of it. In this manner he prepares to await the succors from Gaul, and carry on the war.

Caesar, on learning these proceedings from the deserters and captives, adopted the following system of fortification; he dug a trench twenty feet deep, with perpendicular sides, in such a manner that the base of this trench should extend so far as the edges were apart at the top. He raised all his other works at a distance of four hundred feet from that ditch; [he did] that with this intention, lest (since he necessarily embraced so extensive an area, and the whole works could not be easily surrounded by a line of soldiers) a large number of the enemy should suddenly, or by night, sally against the fortifications; or lest they should by day cast weapons against our men while occupied with the works. Having left this interval, he drew two trenches fifteen feet broad, and of the same depth; the innermost of them, being in low and level ground, he filled with water conveyed from the river. Behind these he raised a rampart and wall twelve feet high; to this he added a parapet and battlements, with large stakes cut like stags' horns, projecting from the junction of the parapet and battlements, to prevent the enemy from scaling it, and surrounded the entire work with turrets, which were eighty feet distant from one another.

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.

After completing these works, saving selected as level ground as he could, considering the nature of the country, and having inclosed an area of fourteen miles, he constructed, against an external enemy, fortifications of the same kind in every respect, and separate from these, so that the guards of the fortifications could not be surrounded even by immense numbers, if such a circumstance should take place owing to the departure of the enemy's cavalry; and in order that the Roman soldiers might not be compelled to go out of the camp with great risk, ho orders all to provide forage and corn for thirty days.