C. Julius Caesar, Gallic War

On discovering these things the chiefs of Britain, who had come up after the battle was fought to perform those conditions which Caesar had imposed, held a conference, when they perceived that cavalry, and ships, and corn were wanting to the Romans, and discovered the small number of our soldiers from the small extent of the camp (which, too, was on this account more limited than ordinary, because Caesar had conveyed over his legions without baggage), and thought that the best plan was to renew the war, and cut off our men from corn and provisions and protract the affair till winter; because they felt confident, that, if they were vanquished or cut off from a return, no one would afterward pass over into Britain for the purpose of making war. Therefore, again entering into a conspiracy, they began to depart from the camp by degrees and secretly bring up their people from the country parts.