C. Julius Caesar, Gallic War

Vercingetorix, when he ascertained the arrival of Caesar, desisted from the siege [of Gergovia], and marched to meet Caesar. The latter had commenced to besiege Noviodunum ; and when embassadors came from this town to beg that he would pardon them and spare their lives, in order that he might execute the rest of his designs with the rapidity by which he had accomplished most of them, he orders their arms to be collected, their horses to be brought forth, and hostages to be given. A part of the hostages being now delivered up, when the rest of the terms were being performed, a few centurions and soldiers being sent into the town to collect the arms and horses, the enemy's cavalry which had outstripped the main body of Vercingetorix's army, was seen at a distance; as soon as the townsmen beheld them, and entertained hopes of assistance, raising a shout, they began to take up arms, shut the gates, and line the walls. When the centurions in the town understood from the signal-making of the Gauls that they were forming some new design, they drew their swords and seized the gates, and recovered all their men safe.