in erecting two walls side by side contemporaneously, such capable builders as the Romans would thus have left one of the bases uncovered, especially in view of the small difference in level. In the clay of the floor, too, were relics of an older period. Moreover, as we have already seen, such vaults have been noted as later additions at Butzbach in Germany and at Brough in England. Once more, the wall dividing the outer from the inner court lay on disturbed soil, and considerably higher than the foundation of the row of pillars to the west. In the outer court the pillars on the south side showed signs of alteration.

It seemed quite plain that we had here two occupations, in both of which the building had had its principal entrance from the same main street on the east. But the early system of ditches could not belong to either of these occupations. Not only did the ramparts of the later occupations lie over them, but the barrack buildings on the east were actually built above them. The south gate of the early fort lay almost at the end of the later Via Quintana, the street which, running parallel to the Via Principalis, crossed the fort immediately to the west of the Principia.

Four Occupations

We were thus in possession of proof of three occupations. So far, however, no evidence was forthcoming to show why, in enlarging the position of the fort, the early entrance to the south had been abandoned, and the line of the Via Principalis moved further to the east. The first definite indication of four occupations was obtained in the excavation of the gates on the south side. At the end of the Via Principalis it was found that the ditches had been filled up with river stones to allow the road to pass over them. In the large ditch immediately in front of the wall, which was undoubtedly later than the first occupation, nine feet of black silt lay below the cobbles. It was clear from this that at an earlier period the ditch at this point must have been open, and that either it must have been crossed by a drawbridge, or there must have existed elsewhere another entrance, which had subsequently been superseded by the road, to carry which the ditch had been filled up. As the Via Principalis of the plan had clearly been used during two occupations, its continuation crossing the ditches at this point, the earlier entrance (if it existed) must have marked an occupation intervening between the oldest occupation of all, with its peculiar gateways, and the two later ones. It must have been an occupation during which a great strengthening of the defences had taken place, and during which the road doubtless passed out on solid ground.