[161] This part of the Jura on the left bank of the Rhone is called the Mont du Vuache.
[162] De Bello Gallico, I. 8.
[163] M. Queypo, in his learned work on the weights and measures of the ancients, assigns to the Roman foot, subdivided into twelve inches, a length of 0·29630m. The Roman pace was five feet, so that the mile was equivalent to a length of 1481·50m.
[164] Dio Cassius says that “Cæsar fortified with retrenchments and walls the most important points.” (XXXVIII. 31.)
[165] The retrenchments which Cæsar calls murus fossaque could not be a wall, in the usual acceptation of the word: first, because a wall would have been but a weak obstacle; further, because the materials were not found on the spot; and lastly, because if so great a quantity of stones had been collected on the bank of the Rhone, we should still find traces of them. I have therefore sought another explanation, and thought that murus might be understood of a natural escarpment rendered steeper by a slight work. Penetrated with this idea, I sought Baron Stoffel, the commandant of artillery, to inspect the localities, and the result of his researches has fully confirmed my suppositions. The following is a summary of his report:—
Considered in its ensemble, from Geneva to the Pas-de-l’Ecluse, the Rhone presents the appearance of an immense fosse from 100 to 120 mètres broad, with abrupt and very elevated scarp and counter-scarp. The parts where it does not present this character are few, and of relatively small extent. They are the only ones where operations for passing the river could be attempted—the only ones, consequently, which Cæsar would have need to fortify on the left bank.
1. From Geneva to the confluence of the Arve and the Rhone, an extent of 1½ kilomètres. Breadth of the river, 90 to 100 mètres.—The left bank is flat in the whole of this extent. The right bank has escarpments almost vertical, the height of which varies from 15 to 35 mètres. (See Plate 3, mean profile between Geneva and the Arve.) No attempt at passage could have taken place, neither at Geneva, nor between the town and the Arve.
2. From the Arve to the plateau of Aire-la-Ville, extent 12½ kilomètres.—After leaving the confluence of the Arve, the heights of the right bank of the Rhone increase in elevation; the escarpments become formidable.—The left bank is bordered with similar escarpments, and the river runs thus between high and abrupt banks, everywhere impassable. It preserves this character to a kilomètre above the ravine of Avril, near Peney. The profiles a a and b b give an idea of the escarpments of the banks from the Avre to the ravine of Avril. (See Plate 3.)—The heights which, on the right bank of the Rhone, extend from Vernier to Peney, sink gradually from one of these villages towards the other, and they form to the east of the ravine of Avril a plateau, the mean elevation of which above the bed of the river is only 20 mètres. Opposite, on the left bank, extends the plateau of Aire-la-Ville. Length 1,700 mètres; breadth, 700 mètres; mean elevation above the bed of the Rhone, 20 to 25 mètres. The heights of the Peney are well disposed for the establishment of an army, and the plateau of Aire-la-Ville would permit an army, the Rhone once passed, to deploy easily. But, in spite of these advantages, it is certain that the Helvetii attempted no operation on this side, for the Rhone flows at the foot of a slope of the height of from 14 to 16 mètres and an inclination of at least 45 degrees.
3. From the plateau of Aire-la-Ville to the point of Epeisses, extent 6 kilomètres.—Down the river from the escarpments of Peney, the heights of the right bank (heights of Russin) form with those of the left bank an immense amphitheatre, nearly circular, the arena of which would be the ground represented green on Plate 3 (diameter, 1½ kilomètres). From the heights of Russin we can descend into the plain to the water of the river. The Rhone, in this part, has never been deep or rapid. The left bank is little elevated, entirely flat opposite the mill of Vert, and the slope of the heights which command it is far from impracticable.
Thus, it was here possible for the Helvetii to effect the passage of the river, and climb the heights of the left bank, if they had not been fortified or guarded. This operation presented least difficulty in the part t t o. And we can hardly doubt that the Romans fortified it to add to the natural obstacles, which were insufficient in this extent. (See the profile c c.)