C. Julius Caesar, Gallic War

The town itself was situated on the top of a hill, in a very lofty position, so that it did not appear likely to be taken, except by a regular siege. Two rivers, on two different sides, washed the foot of the hill. Before the town lay a plain of about three miles in length; on every other side hills at a moderate distance, and of an equal degree of height, surrounded the town. The army of the Gauls had filled all the space under the wall, comprising a part of the hill which looked to the rising sun, and had drawn in front a trench and a stone wall six feet high. The circuit of that fortification, which was commenced by the Romans, comprised eleven miles. The camp was pitched in a strong position, and twenty-three redoubts were raised in it, in which sentinels were placed by day, lest any sally should be made suddenly; and by night the same were occupied by watches and strong guards.