Toward the end of his conquest of Gaul (52 B.C.E.), Julius Caesar cornered the leader of a major uprising in the hilltop town of Alesia. His troops built a ring of fortifications to contain the Gauls in the city, then built another around themselves to fend off the huge relief force that arrived soon. He describes the works himself in his memoir of the Gallic campaign.

Both construction material and, food supplies had to be gathered and great fortifications be built at the same time, despite our reduced forces, which were going further and further from camp. Occasionally, the Gauls tested our defenses and attempted sallies in full force from the town from several gates at a time. As a result, Caesar thought these works needed to be reinforced so they could be defended by a smaller force. Tree trunks and...