He began by clearing away the slopes of the ancient Oppidum along the verge of the plateau, thus removing some of the villæ that had not been destroyed at the time when the arrival of the Germans was expected (see Fig. 16). After having carefully studied the conformation of the ground, he perceived that the front of the city towards the north was weak, inasmuch as this front was most accessible to attack on account of the neighbouring plateau, whose level was but little below that of the site. He determined, therefore, to fall back, so as to get a more extended front. The front thus adopted was three hundred and fifty paces long.[4] Outside of this front he had a fosse sunk twenty feet wide in the bottom,[5] so as entirely to divide the tongue of land which connected the promontory with the northern plateau. This fosse terminated at the two declivities east and west. At each end the bottom of the fosse was furnished with palisades, and there was a descent into the fosse by means of a flight of steps contrived in one of the towers, as will presently be shown. Outside the fosse he formed a _vallum_ about four hundred paces in length, with an outwork containing a guardhouse and a watch-tower. The Roman road to Langres came to this point. On the eastern side, the aqueduct which brought water to the city followed the _vallum_, and was crenelated (_vide_ A). A gate was opened in the north front, flanked on the outside by two cylindrical towers. At the north-west angle arose a square tower high enough to afford a distant view of the valley at the bottom of which runs the river, and of the plateau; another square tower was built at the north-east angle, and between these two towers and the gate two other towers; so that between each tower there remained a space of about eighty feet.