Titurius was instructed to show the greatest possible consideration for the inhabitants, that the neighbouring peoples might not be irritated; and to adhere scrupulously to the terms of the demand transmitted by the envoy—simply to require the surrender of the Helvetii and Catognatus.
On the other hand, his orders were to accomplish the expedition with all possible despatch, as Cæsar had but a few legions with him. The legate, therefore, refrained from investing the city and the Oppidum, and, as he had no reason to fear the immediate arrival of help to the enemy, he judged it best to direct all his efforts to the plateau, hoping to take the fortress by a vigorous effort. It was, however, to be feared that if the Oppidum was taken by assault, Catognatus and a part of the Helvetii might succeed in escaping.
At night, therefore, the legate was devising a plan by which, with the eight thousand men or thereabouts of which his force consisted, he might at the same time prevent all means of escape from within, and make a vigorous attack upon the Oppidum, when a centurion came to tell him that some of the inhabitants requested a private interview with him.
The inhabitants in question were magistrates of the lower town.... Falling at Titurius's feet, they told him with tears that it was with no good will they submitted to the dominion of Catognatus and his warriors; that the demands presented that day to the assembly by the envoy were nothing but reasonable, since the Helvetii had entered Gaul only as marauders, and that Catognatus had used his influence to embarrass the march of the Romans their allies, who had come to destroy the Helvetii; that they the magistrates had no authority over the warriors, and very little over the populace, enthralled as they were, and deceived by the agents of Catognatus; that this chief and his men had taken refuge in the Oppidum, and the part of the town situated at the extremity of the promontory, abandoning the part built on the right bank; that, in fact, they entreated the legate to occupy that part of the city with his troops, who would be well received, and who, they hoped, would not give themselves up to any excesses, since they were treated as friends.
Titurius raised them, and, speaking kindly to them, promised to do what they asked; but, fearing treachery, stated that he must keep them as hostages. The magistrates surrendered themselves to his disposal, declaring that his troops would find the gates open, the posts unoccupied, and the inhabitants in great excitement, but by no means hostile, if they were well treated.
On their arrival, the Romans had instituted a ferry on the river below the town. A reconnoitring party despatched immediately reported that the egresses were in fact free, and that no one appeared behind the walls.
Titurius therefore invested all the egresses, and towards midnight a thousand men selected from among the auxiliaries were in possession of the lower town, without any sound of disturbance or sign of disorder. In the morning the Gallic warriors posted at the head of the bridge saw the Romans before them, and were vehement in their abuse of the inhabitants, threatening to burn the town as soon as they had driven away the Roman troops. Meantime, the Romans demolished several houses adjoining the head of the bridge, and made use of the débris to form a semi-circular intrenchment of contravallation, ending against the river at its two extremities. Titurius established some posts along the rivulet; and on the larger stream above the city he constructed a bridge of boats guarded by two posts at either end. This accomplished, he removed with the bulk of his troops to the northern part of the plateau.
Next day he examined the position, after having filled up a part of the intrenchment; but Catognatus had done away with the egresses of the northern front, and completed the rampart at this point. The assault was vigorously repulsed. This success emboldened the besieged, and they began to overwhelm the legate with sarcasms. Seeing that he could not take the Oppidum by storm, in presence of a determined and numerous body of men, he resolved upon a regular siege.
Although the cutting dug by the defenders between the Oppidum and the plateau was only a bowshot from the rampart, in a few hours it was almost entirely filled up, consolidated, and levelled. Then Titurius had a great number of trees felled in the woods extending along the northern plateau, and brought in front of the camp.
This wood being duly prepared, an agger was commenced fifteen paces from the ramparts, in spite of the darts and stones hurled by the besieged.