The north-east angle tower has been moved when the Wall was built, in order to be in a better position for commanding the line of the Wall, showing that the Wall was not thought of when the fort was built. The slopes to the south outside the south gateway were covered with buildings so closely that there was no room for a man to pass between the walls of the houses; and to the west there are signs of terraced gardens, such as are common now in Italy. There are many traces at Borcovicium of the occupation of the enemy, during which time he has destroyed as much as possible of the buildings and walls; and the Romans on re-entering have built again on the ruins, without removing the débris. This accounts for great differences in floor-levels that are found. I left Borcovicium by the north gate, and followed along the north wall till I came to a little wood, which begins just where the fort ends. The track {124} of the Wall runs through this little wood, almost hidden in lush and lusty grass, on the extreme edge of the basalt cliffs, which are very steep again here. With slight breaks, the best walking is along the top of the Wall all the way from this little wood to Rapishaw Gap; and then again from Cat Stairs to the west end of Peel Crag. A splendid piece of Wall is this that we are now traversing! A quarter of a mile from Borcovicium is what is known as the Housesteads mile-castle, the most perfect specimen of a mile-castle that can be seen to-day above ground. As usual the Wall forms its northern wall, and here it stands fourteen courses, or 9½ feet, high. The thickness of the Wall at the north gateway is not less than 10 feet. The original opening was 10 feet wide, and spanned by an arch, the springers of which are in position still, as also one of the voussoirs; and one of the voussoirs of the arch of the inner gateway is placed on the impost of the outer, as shown in the picture facing this page. Broomlee Lough is seen in the distance. [Illustration: THE NORTH GATE OF HOUSESTEADS MILE-CASTLE SHOWING HOW THE GATEWAY WAS NARROWED IN LATTER ROMAN TIMES] The inner gateway has been made, at a later period, by walling up the original one, and so reducing the width from 10 feet to 3¾ feet, and the floor has been raised 3½ feet above the original level. Everything goes to indicate that the gateway has been destroyed several times, and that the Romans have built it up again without removing {125} the débris. This partial walling-up of the gateways seems to have been done in the case of most of the forts and mile-castles, in the later period of Roman occupation, when Rome could not spare many soldiers for this outlying province.