to lay waste the country and force the Roman garrisons to withdraw as they were gradually starved out. A necessary part of the program was the fighting of a decisive battle on a large scale. Vercingetorix had the men at his command, for he had won over the Ædui, who from the first had aided the Romans in their conquests. Cæsar’s plan was to take the various tribal strongholds one by one; he succeeded in the case of Avaricum, the capital of the Bituriges. He then sent Labienus against Lutetia with four legions, while he advanced with six to lay siege to the chief city of the Arverni, Gergovia. Cæsar’s army was not strong enough for the task; the plan of attack failed, and the Roman legions were saved only by a quick junction with Labienus. The whole army was soon withdrawn from central Gaul in order to protect the Roman province from attack and also to secure for Cæsar a position where he could establish a fortified camp, from which it would be difficult to be dislodged, and where he could depend upon a regular source of supplies. He selected a place on the Saône, where he could threaten the Æduan territory and be so protected that it would be dangerous for Vercingetorix to follow him. On the march the Romans were vigorously attacked by the Gallic cavalry, but, as they had with them a detachment of German horse, they were beaten off, and the Romans quickly turned the tables, pursuing the Gallic army and finally enclosing it in a hill town, Alesia (Alise Ste. Reine). Preparations were now made for a long siege. It was a complicated affair, because Cæsar had to provide against attacks both from the beleaguered army and from the Gauls, who were hastening to aid their natural champion. The lines of contravallation were sixteen kilometers long, those of circumvallation twenty; the space between the Roman army and the town was filled with artificial obstacles, meant to prevent the successful use of infantry. The force under Cæsar numbered about 70,000 men and included eleven legions. Cæsar reports that there were 80,000 men imprisoned in Alesia, while to the Gallic relief army is assigned 250,000 infantry and 8000 cavalry. Probably there were not more than 20,000 men altogether in Alesia, for provisions were scarce. This is the number that Napoleon I would give to the inclosed army, and he further remarks that the relief army in its manœuvering and in its camping operations behaved as if it were equal, not superior in strength, to its adversaries.