History of Julius Caesar Vol. 2 of 2. Napoleon III

plain slightly inclined towards the river. It is marked by a green tint on Plate 3. People can descend from all sides and approach the Rhone, the bank of which is flat. Opposite, the left bank presents insurmountable obstacles until below Cologny, at s. But below this point, from s to y, the bank is flat, and the heights situated behind are accessible on an extent of 2 kilomètres.

The Helvetii, established on the heights of Pougny and Colonges, could descend to the Rhone, and cross it between Etournel and the hamlet of Les Isles. The Romans had thus to unite the escarpments which terminate at Cologny with the impracticable slopes of the mountain of Le Vuache. Here again we shall see that they took advantage of the peculiarities of the ground.

At the village of Cologny, the heights form a triangular plateau, s u x, of which the point s advances like a promontory towards the Rhone, which it commands perpendicularly by at least 20 mètres. A projection of land, s u, bounds it in front, and separates it from a plain which extends to the river. The escarpment produced by this projection of land presents to the Rhone a slope of about 45 degrees. It rises over the plain about 14 mètres towards its extremity s, but diminishes gradually in height, until it is only 2 to 3 mètres in height near the point u. (See the profile n n.) The Romans hollowed, on the slope of the escarpment from s to u, a length of 800 mètres, a trench forming wall and fosse. The plateau of Cologny, situated in the rear, offered a favorable position for the defence of this retrenchment. (See the profile p p.) They prolonged their works towards the west as far as y; beyond that, the heights presented sufficient natural obstacles. We may thus estimate that, from Cologny to the mountain of Le Vuache, the Romans executed from 1,600 to 1,700 mètres of retrenchments.

To sum up: the works executed on five principal points, between Geneva and the Jura, represent a total length of about 5,000 mètres, that is, less than the sixth part of the development of the course of the Rhone.

Admitting that Cæsar had at his disposal 10,000 men, we may suppose that he distributed them in the following manner: – 3,000 men on the heights of Avully, his head-quarters; 2,500 at Geneva; 1,000 on the plateau of Aire-la-Ville; 2,000 at Chancy; and 1,500 on the plateau of Cologny. These 10,000 men might be concentrated: in two hours, on the heights between Aire-la-Ville and Cartigny; in three hours, on the heights of Avully; in three hours and a half, on the plateau of Chancy; in three hours and a half, these troops, with the exception of those encamped at Geneva, might be brought together between Cologny and the fort of L’Ecluse. It would require five hours to carry the detachment from Geneva thither.

The detachments mentioned above, with the exception of that of Geneva, were established in what Cæsar calls the castella. These were constructed on the heights, in the proximity of the retrenchments which had to be defended – namely, at Aire-la-Ville, Avully, Chancy, and Cologny. They consisted probably of earthen redoubts, capable of containing a certain number of troops. They are represented by squares in Plate 3.

Cæsar could reconnoitre every instant the march and designs of the Helvetii, the heights of the left bank of the Rhone presenting a great number of positions where it was easy to place advantageously posts of observation. Commandant Stoffel has pointed out six, which are marked on Plate 3. As it will be observed, the Helvetii, in crossing the Rhone, could not be disturbed by darts thrown from the top of the retrenchments, for these darts would not carry to the left bank of the river. Now there exists at present, between this bank and the foot of the heights in which these trenches were cut, flat ground of more or less extent. Admitting, then, that the Rhone flowed nineteen centuries ago in the same bed as at the present day, we may ask if the Romans did not construct, in these low parts near the bank, ordinary retrenchments, composed of a fosse and rampart. The excavations undertaken by the Commandant Stoffel have revealed everywhere, in these plains, the existence of ground formed by alluvium, which would lead us to believe that the Rhone once covered them. However, even if at that epoch these little plains had been already uncovered, either wholly or in part, we can hardly suppose that Cæsar would have raised works there, since the heights situated in the rear permitted him, with less labour, to create a more redoubtable defence – that of the trenches opened along the crests. As we see, the obstacle presented to the assailants began only with these trenches, at the top of the slopes.

As to the vestiges which still appear to exist, they may be described as follows. The slopes which the Romans fortified at Chancy, from k to z, and at Cologny, from s to y, present, in the upper parts, in some places, undulations of ground, the form of which denotes the work of man. On the slope of Chancy, for instance, the ground presents a projection, i i (see the profile h h), very distinctly marked, and having the remarkable peculiarity that it is about 11 feet high and 8 to 9 feet broad. Now, is it not evident that, if one of the fosses which have been described should get filled up, either naturally, by the action of time, or by the processes of agriculture, it would take absolutely the form i i, with the dimensions just indicated? It would not, therefore, be rash to consider these peculiarities of the ground, such as i i, as traces of the Roman trenches.

We must further mention the projection of land v r, situated below Cartigny. Its form is so regular, and so sharply defined, from the crest to the foot of the talus, that it is difficult not to see in it the vestiges of a work made by men’s hands.

It is easy to estimate approximately the time which it would have taken Cæsar’s troops to construct the 5,000 mètres of trenches which extended, at separate intervals, from Geneva to the Jura.

Let us consider, to fix our ideas, a ground A D V, inclined at 45 degrees, in which is to be made the trench A B C D. The great wall A B C had 16 Roman feet in elevation: we will suppose that A B was inclined at 5 on 1, and that the small wall D C was 6 feet high.

The amount of rubbish removed would be as follows: – Section A B C D = 64 square feet, or, reducing it into square mètres, A B C D = 5 square mètres 60 centimètres.

The mètre in length of the earth thrown out would give thus 5·60 cubic mètres.

If we consider the facility of labour in the trench, since the earth has only to be thrown down the slope, we shall see that two men can dig three mètres in length of this trench in two days. Therefore, admitting that the 10,000 men at Cæsar’s disposal had only been employed a quarter of the time, from two to three days would have been sufficient for the execution of the complete work.