John Mylne, begun 1665-7, rebuilt 1781. Roughly pentagonal ramparts with bastions at corners enclosing complex of predominantly 18th century buildings (some with later alteration) with lime harled walls and droved sandstone ashlar dressings.
WALLS: random rubble with flagged wallhead, E wall battered to Commercial Street, W wall buttressed on E side.
MAIN (WEST) GATE: ashlar surround to N side comprising base course, string course at arch springers, keystone centring arch-head with cornice above. Deep flanking buttresses to E side, 2-leaf vertically-boarded timber gates.
SOUTH GATE: round-arched roll-moulded original arch, rubble infilled with margined door at centre, architraved surround to blank panel centred above. Wall buttressed to N side with segmental relieving arch supporting bridge over.
NORTH GATE: Plain round-arched entrance with rubble voussoirs and 2-leaf vertically-boarded timber gates.
WEST PILE: 2-storey, 11-bay symmetrical barrack block of double pile plan on sloping site. Base course, margined windows and doors.
E (ENTRANCE) ELEVATION: flush-panelled timber entrance door, margined, with heavy bracketted cornice above centring elevation, blank at 1st floor. Regular fenestration in flanking bays, penultimate and outer bays at left and right advanced with taller storey heights.
N ELEVATION: door centring elevation at ground with window above; blank bays flanking.
W (REAR) ELEVATION: 10-bay near-symmetrical elevation, doorways flanking centre bay at ground, regular fenestration at 1st floor with segmental-arched lintels. Doorways at ground in bays to outer left and right with additional window inserted to left of latter.
S ELEVATION: mirrored image of N elevation.
12-pane timber sash and case windows, grey slate M-roof with cast-iron gutters and downpipes. Paired harled stacks with deep ashlar copes, ashlar skew copes.
NORTH PILE: 2-storey, 7-bay asymmetrical barrack block of double-pile plan on sloping site comprising 5-bay near-symmetrical building extended to W by 2 wider additional bays.
S (ENTRANCE) ELEVATION: 7 bays, grouped 2-5. Doorway at ground in bay to outer left offset to right and adjacent to harled stair accessing door at 1st floor in penultimate bay to left. Regular fenestration in bays grouped to right, door at ground in penultimate bay to left.
E ELEVATION: M-gable, with doors centring each at ground.
N (REAR) ELEVATION: asymmetrical, grouped 5-2. 5-bay group symmetrical with door at 1st floor in centre bay. 2-bay group blank at ground.
W ELEVATION: irregularly fenestrated M-gable.
12-pane timber sash and case windows, grey slate M-roof, harled stacks with copes and circular cans; ashlar skew copes.
OUT-HOUSE: harl-pointed random rubble walls, gabled N elevation with vertically-boarded timber door at upper level, narrow window to left of centre with vertically-boarded timber door to outer left, single 16-pane timber fixed-light in W elevation to right of centre. Grey slate roof, piended at S end, stugged and coped sandstone ridge stack, ashlar skew copes.
SOUTH PILE: single storey 11-bay range on sloping site. Random rubble N elevation, harled at 2 bays set back at outer right, and at side and rear elevations. 2-leaf vertically-boarded timber doors at centre bay, 12-pane timber sash and case windows in flanking bays, vertically-boarded timber doors in flanking bays, 12-pane timber sash and case windows in flanking bays and at bay flanking to left, 9-pane in bay flanking to right, vertically-boarded timber doors in bays to outer left and right. Grey slate piended roof with harled and coped ridge stacks.
Random rubble store adjacent to W elevation; gabled 2-bay N elevation with vertically-boarded timber door in bay to left, 6-pane timber sash and case window in bay at right; louvered square opening in gablehead. Single-flue stugged sandstone wallhead stack centring E elevation.
RESERVOIR: single storey random rubble building, platform roof with pitches flanking to E and W. N elevation; door at centre, 2-leaf doors in bay to left, door with flanking infilled openings in bay to right.
E elevation, single window at centre. S elevation; single window to outer right.
POWDER MAGAZINE: harl-pointed and coped rubble wall enclosing submerged and flagged courtyard with shifting room at SE corner and magazine at centre. Shifting room gabled with 2 evenly spaced square windows in W elevation and door centring N elevation. Gabled magazine with slit windows centring each elevation and doors flanking at outer left and right of S elevation.