Type: Fort, Fortlet, Camp, Watch-tower
|Probable Military Road: SW (9) to Bertha
Probable Military Road: NE (10) to Cardean (Tayside)
Probable Military Road: NE (3.5) to Inchtvthil (Inchtuthil, Tayside)
SW (7.5) to Grassy Walls
Although nothing remains of this site beside the Bridge of Isla, the fort platform may be viewed from the minor road leading to the Blackhill signal station, which was itself off-bounds during my visit in April 2004 being enclosed within a young pine plantation used for grouse-breeding. The reason for its construction was apparent enough, there being a direct line-of-sight to the nearby fort.
This first-century (probably Flavian) fort lies at the crossing of the River Isla just to the south of Inchtuthil, an undated fortlet also lies nearby (see below). Although the Cargill fort and the Inchtuthil fortress undoubtedly served different functions and therefore may have been contemporary, their close proximity probably points to one structure preceeding the other, most likeley the smaller Cargill camp first. How the nearby fortlet fits into the scheme of things has yet to be determined.
The Cargill fort was discovered from the air (by CUCAP) in 1977 lying on the left bank of the River Isla just above its confluence with the Tay. The fort is aligned to the north-west, facing the crossing of the Isla and has an attached annexe on the north-west. The minor axis was proved by excavation (in 1980 and 1981) to measure 340 ft. (c.104 m) in width, while the major axis can only be estimated at about 640 ft. (c.195 m), giving an area of just under 5 acres (c.2 ha). The fort rampart, about 20 ft. (6 m) wide, was of clay and turf resting on a corduroy of timber which in places survived to a height of six or seven courses; it had been rebuilt in places using layers of turf interleaved with layers of gravel and/or clay. A berm 8 ft. (2.4 m) wide separated the rampart from the innermost ditch, 10½ ft. wide by 7¼ ft. deep (3.2 x 2.2 m), a median ditch with a similar profile lay 20 ft. (6 m) beyond, and the third and outermost ditch, 12 ft. wide and 6 ft. deep (3.7 x 1.8 m), lay 27 ft. (8.2 m) further out.
The internal buildings, which have been partially excavated, were of timber and included a granary at least 81 ft. (24.69 m) long and 30 ft. (9.1 m) wide with a loading platform fronting onto the via principalis. Like the rampart, there are signs of at least two phases in the interior buildings. A spread of heavy cobbles representing the intervallum road or via sagularis was also noted during trenching across the interior of the fort. The ditches have "parrot-beak" inturnings at the gateways, which have been found at several known Flavian forts in Roman Scotland. Pottery recovered from the site include two sherds of Flavian mortaria.
Beneath all of the Roman occupation levels there are signs of pre-Roman plough ruts, which probably explains the elaborate defensive system surrounding the fort, as the encampment had apparently been placed upon land previously cultivated by the local native tribe, the Venicones. A section across the north-west defences in 1981 revealed that the rampart had been twice repaired, having been damaged at least once by fire when the timber buildings in the annexe were burnt down; there were similar evidence of burning recorded within the fort itself during excavations the previous year. A small assemblage of burnt Samian-ware was found outside the south-west gateway. The evidence suggests that the fort was abandoned in, or shortly after 85AD.
Discovered from the air by Flight-Lieutenant E. Bradley in the early 1940's and confirmed by Prof. St. Joseph in the latter half of the 50's, this small fort or fortlet overlooks the confluence of the Isla with the Tay. The layout is similar to that at Kaims Castle, measuring about 320 ft. from north-east to south-west by 230 ft. transversely (c.97 x 70 m), covering an area of a little under 1¾ acres (c.0.7 ha). Examination of the defences in 1965 showed they consisted of a clay rampart fronted by two ditches, the inner 8½ ft. wide by 4½ ft. deep (2.6 x 1.4 m), the outer 5 ft. wide and 3½ ft. deep (1.5 x 1 m); the outer ditch had been allowed to silt up but the inner ditch had been back-filled with clay, no doubt from the destruction of the rampart when the fortlet was abandoned. All interior details have been erased by the plough.