Completely surrounding the four quadrangles, and enclosing around them a vacant space, varying in width from 25 to 30 yards opposite the cross roads, to as many feet at the abutting angles of each quadrangle, was the prison wall. This in the earlier years was a strong stockade fence, and is so represented in the three earlier plans reproduced in the plates; but at a later date it was replaced by the brick wall shown in Macgregor’s plan, and it is described in the auctioneer’s catalogue of the sale, when the prison and its contents were disposed of in September 1816, as “a substantial brick wall measuring 3,740 feet round, and containing 282 rods of brickwork more or less.” Of this wall, 30 yards are still standing, forming a portion of the garden wall of the house originally occupied by the superintendent. The auctioneer’s description does not altogether agree with that of the surveyor Mr. Fearnall, who in 1813 reported that it was “very indifferently built, and not of the best materials,” and that much of it was in danger of falling, owing to the excavation at its foot within the enclosure of a ditch. This ditch, for its full length of nearly three-quarters of a mile, can be traced at the present day, with the deep embrasures shown in the plans, at each of the four prison gates. It was, at the time the buildings were demolished, about 9 yards wide and 5 feet deep, and it was paved with stone flags; this is supposed to be the “silent walk” of the sentries, excavated in 1809. An item in the barrack master’s accounts for July in that year is £420 19_s._ 6_d._, for the making a walk for the “silent sentries.” The area of the actual prison enclosed within the wall was in 1816 sold in one lot, and is described in the catalogue as “containing by admeasurement 22 acres, 2 roods, and 14 perches more or less.” [Picture: Plate V.—The Inner Side of the Prison Wall as it now Stands] In the boundary wall were four gates, opening on to the ends of the cross streets, which separated the four quadrangles. The north gate opened into a space at the back of the prison occupied by sheds and other accessories; the east and west gates on roadways which ran between the military barracks and the prison from the Peterborough Road; the south gate was opposite the central main entrance from that road into the Depot. Later, as shown in Macgregor’s plan, there were, in addition to these four large gates, a door in the south wall adjoining the house of the agent, or superintendent, and another in the north wall, giving admission to a court outside the wall, in which had been erected a separate prison for the boys. At each gate outside the prison wall was a guard house, a one-storied building fitted with separate rooms for the officers and men of the guard, with cells for prisoners, and with a wide-open shelter, or verandah, in front.