The whole eastern slope of the mountain, that which looks towards Vayrac and the Dordogne, is surmounted with rocks, which have a height of as much as forty mètres; consequently, no operation took place on this side during the time of the siege. The western slope alone was the theatre of the different combats. Its declivities are not inaccessible, especially between the village of Loulié and the hamlet of Leguillat, but they are sufficiently abrupt to make the Latin author say: _Quo, defendente nullo, tamen armatis ascendere esset difficile_. At the very foot of this declivity, and at 200 mètres beneath the culminating point of the plateau, the Tourmente flows, a little river ten mètres broad, embanked between this declivity and that of the opposite heights: _Flumen infimam vallem dividebat_, &c. Such a disposition of the localities, as well as the slight descent of the Tourmente (one mètre in 1,000), rendered it impossible to turn off that river. (_Hoc flumem averti loci natura prohibebat_, &c.) There is no spring on the plateau of Puy-d’Issolu; but several issue from the sides of the mountain, one of which, that of Loulié, is sufficiently abundant to provide for the necessities of a numerous population. This was the spring which the Romans succeeded in turning off. At the time of the siege, it issued from the side of the mountain at _S_ (_see Plate 31_), at twenty-five mètres from the wall of the _oppidum_, and at a distance of about 300 mètres from the Tourmente. These 300 mètres make about 200 Roman paces. We see, therefore, that in the Latin text the word _pedum_ must be replaced by _passuum_. We also see that the word _circuitus_ (VIII. 4) must be taken in the sense of the _course_ of the river. The “Commentaries” say (VIII. 33) that Rebilus established three camps in very elevated positions. Their sites are indicated by the nature of the localities: the first, _A_, was on the heights of Montbuisson; the second, _B_, on those of the Château de Termes; the third, _C_, opposite the defile of Roujon, on the Pech-Demont. It appears from the excavations that the Romans had not retrenched the two first, which is easily explained, for the heights to the west of the Puy-d’Issolu are impregnable. Moreover, the Romans at Uxellodunum were not in the same situation as at Alesia. There they had before them 80,000 men, and in their rear a very numerous army of succour; here, on the contrary, it was only a question of reducing a few thousand men. The camp _C_ required to be protected, because it was possible for troops to descend from the tableau of the Puy-d’Issolu towards the defile of Roujon, which, being situated fifty mètres lower down, gives an easy access to the heights of Pech-Demont. The excavations have, in fact, brought to light a double line of parallel fosses, which barred the defile behind, and formed at the same time a countervallation.