CIRCUMVALLATION.--Over the extent of the plain of Laumes, and on the slopes of the mountain of Flavigny, the circumvallation was parallel to the countervallation, at a mean distance of 200 mètres. It had only one single fosse, which in the plain was square-bottomed, so as to allow more soil to be dug out; everywhere else its form was triangular. (_See Plate_ 28.) The circumvallation of the mountain of Flavigny ceased towards the escarpments, where the defences became useless; then, again, it continued on the plateau, where it formed the connection between the camps. After this, it descended towards the Oserain, cut the point of Mont Penneville, re-ascended the slopes of the mountain of Bussy, where it similarly united the camps, descended into the plain of Grésigny, which it crossed in a direction parallel to the countervallation, and ended at camp _D_. On the heights it was made to follow the undulations of the ground, so that its defenders should occupy as much as possible a commanding position with respect to that of the assailants. Moreover, the works of the circumvallation were not everywhere the same. Thus, near the escarpments and ravines which cut this line, the Romans had made no fosse with epaulment, but only accessory defences, such as _abatis_ and wolf-pits, which even alternated on divers points. Above the _castellum_ 21, between Grésigny and Mont Réa, the excavations have brought to light a fosse of great dimensions, the bottom of which was full of bones of animals of divers kinds. Its position, near a small ravine in which runs a brook, may lead us to suppose that here was the _abattoir_ of the Roman army. In considering this fosse, and those which have been discovered on the top and on the slopes of Mont Réa, as forming part of the circumvallation, there will be found for the development of this line about twenty kilomètres, which represents with sufficient accuracy the fourteen miles of the text of the “Commentaries.”[539] WOLF-PITS.--In the plain of Laumes, at the top of the circumvallation, and close to the exterior bank of the fosse, there have been counted more than fifty wolf-pits, in five rows. Others have been cleared out on the heights--nine between the camp _A_ and the escarpments, twenty-seven on the mountain of Bussy, near the _castellum_ 15; they are dug in the rock, and in such a perfect state of preservation that they appear as though they had been made but yesterday. At the bottom of some of these last, fifteen arrow-heads were picked up. All these wolf-pits are three feet deep, two feet in diameter at the top, and a little less than one foot at the bottom.