The inner harbour of Boulogne was approached by a narrow channel dividing the north-eastern from the south-western cliffs; and the waters of the bay, flowing through it and uniting with the River Liane in covering the present site of the lower town, rushed onwards as far as the valley of Tintelleries and the vale of St. Martin. Facing the site of the present town there was an island called Elna, and on it was built the ancient town of Gessoriac, which was connected with the mainland by a bridge. Realising the future importance of the place both for naval and military purposes, Caesar commissioned Pedius, a native of Bononia, in Italy, to lay out a town on the declivity of the Grande Rue, leading to Haute Ville, as the upper town and the hill leading to it are called at the present day. (Bertrand's "History of Boulogne-sur-Mer," pp. 17, 18. "Walkernaer's Geography," vol. i., p. 454). The walls of the present fortifications of Haute Ville, built in the thirteenth century, rest on the ancient foundations of the old Roman encampment. This fact was proved at the time when a tunnelling was made for the railway from Boulogne to Calais under Haute Ville ("Dictionnaire Historique et Archeologique du Pas de Calais," vol. i, p. 22). The circuit of the present fortifications, about 700 yards square, present to-day the appearance pf the old Roman encampment. "The camp of a Roman legion," writes Gibbon, "presented all the appearance of a fortified city. As soon as the place was marked out, the pioneers carefully levelled the ground and removed every impediment that might interrupt its perfect regularity. It forms an exact quadrangle, and we might calculate that a square of 700 yards was sufficient for the encampment of 20,000 Romans, though a similar number of our troops would expose to an enemy a front of more than treble its extent. In the midst of the camp the pretorium, or general's quarters, rose above the others; the cavalry, the infantry, and the auxiliaries occupied their respective stations; the streets were broad and straight, and a vacant of 200 feet was left on all sides between the tents and the ramparts. The rampart itself was usually twelve feet high, and defended by a ditch twelve feet in depth, as well as in breadth. This important labour was performed by the legionaries themselves, to whom the use of the spade and the pick-axe was no less familiar than the sword and the pilum" ("Decline and Fall of the Roman Empire," vol. i., p. 27.) This gives a faithful description of the Roman encampment (Castra Stativa) at Boulogne, which is described by St. Patrick as Bonaven Tabernise, or Bononia, where the Roman encampment was pitched. Bononia, according to Bertrand's "History of Boulogne," was regarded by the Romans as their "principal dockyard" in Northern Gaul; and Suetonius, in his "Lives of the Twelve Caesars," describes it "as the port from which the Roman legions successively departed for Britain" (p. 283, note).