Moreover, it was known everywhere amongst the Gauls that Cæsar had only one summer more to hold his command, and that after that they would have nothing more to fear. He left, therefore, the lieutenant Quintus Calenus[552] at the head of his two legions, with orders to follow him by ordinary marches, and with his cavalry he hastened by long marches towards Uxellodunum. Cæsar, arriving unexpectedly before that town, found it completely invested on all accessible points. He judged that it could not be taken by assault (_neque ab oppugnatione recedi videret ulla conditione posse_), and, as it was abundantly provided with provisions, he conceived the project of depriving the inhabitants of water. The mountain was surrounded nearly on every side by very low ground; but on one side there existed a valley through which a river (the Tourmente) ran. As it flowed at the foot of two precipitous mountains, the disposition of the localities did not admit of turning it aside and conducting it into lower channels. It was difficult for the besieged to come down to it, and the Romans rendered the approaches to it still more dangerous. They placed posts of archers and slingers, and brought engines which commanded all the slopes which gave access to the river. The besieged had thenceforth no other means of procuring water but by fetching it from an abundant spring which arose at the foot of the wall, 300 feet from the channel of the Tourmente. (_See Plate 31._) Cæsar resolved to drain this spring, and for this purpose he did not hesitate to attempt a laborious undertaking: opposite the point where it rose, he ordered covered galleries to be pushed forwards against the mountain, and, under protection of these, a terrace to be raised, labours which were carried on in the middle of continual fights and incessant fatigues. Although the besieged, from their elevated position, fought without danger, and wounded many Romans, yet the latter did not yield to discouragement, but continued their task. At the same time they made a subterranean gallery, which, running from the covered galleries, was intended to lead up to the spring. This work, carried on free from all danger, was executed without being perceived by the enemy; the terrace attained a height of sixty feet, and was surmounted by a tower of ten stories, which, without equalling the elevation of the wall, a result it was impossible to obtain, still commanded the fountain. (_See Plate 32._) Its approaches, battered by engines from the top of this tower, became inaccessible; in consequence of this, many men and animals in the place died of thirst. The besieged, terrified at this mortality, filled barrels with pitch, grease, and shavings, and rolled them in flames upon the Roman works, making at the same time a sally, so as to prevent them from extinguishing the fire; soon it spread to the covered galleries and the terrace, which stopped the progress of the inflammable materials.