DISTRIBUTION OF THE ARMY. DEVELOPMENT OF THE LINE OF INVESTMENT.--We know, from the “Commentaries,” that camp _D_, on the slopes of Mont Réa, contained two legions. By comparing its superficies with that of the other camps, we may admit that these were occupied in the following manner: in camp _A_, one legion; in camp _B_, two legions; in camp _C_, three legions; total, eight legions. The three remaining legions would have been distributed in the twenty-three redoubts. As we have said, the number of 11,000 paces can evidently only apply to the line of investment formed by the eight camps and the twenty-three redoubts established round Alesia immediately after the arrival of the army, and not, as has been believed, to the countervallation properly so called, which was only constructed subsequently (VII. 72). This number is rigorously exact, for the circuit of ground surrounded by the camps measures a little more than sixteen kilomètres, which represents 11,000 Roman paces. THE FOSSE OF TWENTY FEET.--This fosse has been discovered in its whole extent: it barred the plain of Laumes, following a direction perpendicular to the course of the Ose and the Oserain, and did not go round Mont Auxois. _Plate 28_ represents two of its most remarkable sections. It was not exactly twenty feet in width, as stated in the “Commentaries;” neither was it everywhere 400 paces distant from the countervallation. This measurement is only exact towards the extremities of the fosse, near the two rivers. COUNTERVALLATION.--Vercingetorix, having retired to the plateau of Alesia, could only have escaped by the plain of Laumes, and, at the worst, by the valley of the Rabutin; for the spurs situated to the south, the east, and the north of Mont Auxois are surmounted by a belt of perpendicular rocks, which form insurmountable barriers, and the valleys of the Oserain and the Ose, which divide them, constitute veritable defiles. It became important, therefore, to bar the plain of Laumes with impregnable works. Hence Cæsar accumulated there the means of defence; but he simplified them everywhere else, as the excavations have shown.