Caesar - Gallic War- Book VII, 68 - Alesia (Alise-Sainte Reine)
After making the whole chivalry flee away, Vercingetorix drew back the army as he had put it in front of the camp, and started to march towards Alesia, which is the capital of the Mandubii, and ordered his soldiers to transport the luggages out of the camp and to follow him quickly. After the luggages were taken to a nearby hill and given in custody of two legions, Caesar chased the enemy as long as the duration of the day allowed him to and killed about 3.000 people of the back of their army; the following day he set the camp near Alesia. After examining the location of the city and after terrifying the enemies, as chivalry, which was the sector they trusted most, had fled away, Caesar exorted the soldiers to work and started to build a trench around the city.
Caesar - Gallic War- Book VII, 69 - Alesia (Alise-Sainte Reine)
The actual stronghold of Alesia was set atop of a hill, in a very lofty situation, apparently impregnable save by blockade. The bases of the hill were washed on two separate sides by rivers. Before the town a plain extended for a length of about three miles ; on all the other sides there were hills surrounding the town at a short distance, and equal to it in height. Under the wall, on the side which looked eastward, the forces of the Gauls had entirely occupied all this intervening space, and mad made in front a ditch and a rough wall six feet high. The perimeter of the siege works which the Romans were beginning had a length of eleven miles. Camps had been pitched at convenient spots, and twenty-three forts had been constructed on the line. in these picketts would be posted by day to prevent any sudden sortie ; by night the same stations were held by sentries and strong garrisons.