OSMap: LR124, OL18
Type: Fort, Practice Works, Amphitheatre.
N (12) to Bryn y Gefeiliau (Gwynedd)|
Possible road: WNW (14) to Pen Llystyn (Gwynedd)
SSE (14) to Brithdir (Gwynedd)
|SH705387||c.510 x 390 ft|
(c.155 x 120 m)
First recorded as Roman by the antiquary Robert Vaughan around 1630, the first plan was published by Pennant in 1781 and the first excavations were conducted in 1850 and 1868. This fort stands on a small prominence on the eastern side of Ffestiniog Vale about half way down the slopes of Myndd Maentwrog overlooking the Llyn Trawsfynydd from the north-east. A small stream passes just outside the south-eastern defences and feeds into the lake next to the site of the nuclear power station. The site is nowadays dominated by a Norman motte, and it is possible that the fort's defences acted as this Medieval castle's outer enclosure or bailey.
Rectangular in outline with rounded corner-angles, the Roman fort measures 510 feet WNW-ESE by 390 feet transversely (c.155 x 120 m), covering an area of just over 4½ acres (c.1.7 ha). Gateways are recorded in the middle of the south-east defences and in the south-west defences off-set to the east by a ratio of about 3:2, which is the typical Roman military tertiata pattern; the fort therefore faced east-south-east.
Dating evidence suggests that the fort was built by governor Gnaeus Julius Agricola c.A.D.78, and was slightly reduced in size c.110, when the walls were rebuilt in stone. It was finally abandoned c.140 and never re-occupied. The latest piece of Samian recorded at the site was of "Potter X-6", who produced wares c.A.D.125-150; two pieces of decorated ware were dated c.100-120.
Many features have been observed from the air. A cross-ditch at the north-west end of the fort reduced the occupation area by about one-fifth. An annexe measuring about 175 by 150 feet (c.53 x 46 m) and enclosing an additional ½-acre (c.0.24 ha), was attached to the northern end of the north-western defences. The outline of a stone-built principia measuring about 80 x 85 feet (c.24 x 26 m) and facing south-east in the centre of the fort, was observed from the air as parch-marks in the dry Summer of 1976; other internal features were also observed at the same time.
A small oval earthwork to the north-east of the fort "said to measure twenty-seven by thirty-seven yards" (c.24.6 x 33.8 m), has been described as a Roman amphitheatre perhaps built to compensate the troops for being posted to such a remote location; this identification remains doubtful. Close by is an area of levelled ground thought to have been a parade ground.
Two military practice works have been identified some 350 feet (c.107 m) to the north-west of the fort. The nearest measures about 55 by 54 feet (c.16.7 x 16.4 m) and has a well-preserved rampart, ditch and upcast counterscarp; there are two opposing gateways defended by tutulus outworks. Another smaller camp, lying about 150 feet (c.46 m) from its larger companion and measuring about 36 by 35 feet (c.11 x 10.7 m), has a single entrance gap in its defences.
There are two more "practice works" nearby along the Nant Twll y Cwm to the east at Braich Ddu (SH7138), also five more at Dolddinas about 2 miles (c.3 km) to the east-south-east in the valley of the Afon Llafar (SH7337).
Haverfield records nine stones in the structure of Harlech Castle bearing inscriptions in Latin, which reputedly originated from the Tomen-y-Mur fort. All are recorded below:
|(1)||> A N D P XXXIX||"The century of And[... has built] thirty-nine paces [of rampart wall]."|
|(2)||> IVLI MANS||"The century of Julius Mans[uetus?]."|
|(3)||> PERPE TVI P XX||"The century of Perpetuus [built] twenty paces."|
|(4)||> IVL PERPETVI P XXI||"The century of Julius Perpetuus [built] twenty paces."|
|(5)||> PERPETVI P XXII||"The century of Perpetuus [built] twenty-two paces."|
|(6)||> IVLI PERPETVI P XXXIX||"The century of Julius Perpetuus [built] thirty-nine paces."|
|(7)||> PERPE P X X [...]||"The century of Perpetuus [built] twenty[?...] paces."|
|(9)||PRC[?...]||"Pro[-praetorian governor? ...]"|