Julius Caesar Gallic War 7.9

Caesar, having delayed two days in that place, because he had anticipated that, in the natural course of events, such would be the conduct of Vercingetorix, leaves the army under pretense of raising recruits and cavalry: he places Brutus, a young man, in command of these forces; he gives him instructions that the cavalry should range as extensively as possible in all directions; that he would exert himself not to be absent from the camp longer than three days. Having arranged these matters, he marches to Vienna by as long journeys as he can, when his own soldiers did not expect him. Finding there a fresh body of cavalry, which he had sent on to that place several days before, marching incessantly night and day, he advanced rapidly through the territory of the Aedui into that of the Lingones , in which two legions were wintering, that, if any plan affecting his own safety should have been organized by the Aedui, he might defeat it by the rapidity of his movements. When he arrived there, he sends information to the rest of the legions, and gathers all his army into one place before intelligence of his arrival could be announced to the Arverni. Vercingetorix, on hearing this circumstance, leads back his army into the country of the Bituriges; and after marching from it to Gergovia , a town of the Boii, whom Caesar had settled there after defeating them in the Helvetian war, and had rendered tributary to the Aedui, he determined to attack it.