Tomen y Mur represents one of the premier archaeological landscapes in the Welsh uplands, and one of the most complete Roman military complexes in Britain. Much has been recorded over the years by archaeologists and surveyors on the ground. Gresham's 1938 paper on the fort established the first accurate survey of the site, including ancillary earthworks of interest, and drew together the numerous antiquarian observations made by Pennant, Fenton, Sir Richard Colt Hoare and others.

Tomen-y-Mur is a Roman military settlement set on a mountain shoulder overlooking the Trawsfynydd basin. It was established in the late first century and occupied into the second century if not later. The site continued to be important into the early medieval period and the fort defences may have been refortified, possibly when Norman armies encamped here in the late eleventh-early twelfth century. The 'Tomen', the great castle mound (NPRN 95478), was probably raised in the twelfth or thirteenth century and may have been associated with a llys or princely court.

Occupation on the site lasted into the twentieth century and, owing to its remote upland location, it presents an unparalleled array of earthworks belonging to these various periods. It is the best preserved Roman military settlement in Wales. Antiquarian investigations began in the nineteenth century and the site is now presented by the Snowdonia National Park Authority who have reconstructed a section of the fort wall. The military settlement centres on the fort enclosure which is laid out across the south-eastern slopes of a low isolated ridge. To the south-east are the remains of several buildings including a probable bathhouse (NPRN 89400), as well as a bridge abutment (NPRN 89467). To the east is a large levelled parade ground (NPRN 89404) overlooked by a great monument, possibly a temple complex (NPRN 89401-3). Beyond these is what appears to be a small amphitheatre (NPRN 95666). There are various burial mounds around the fringes of the settlement (see NPRN 95479, 89408-9), one of which (NPRN 89420) overlies a Roman road (NPRN 89468) and may be early medieval.

Sources:
Crew, P. & Musson, C. 1996. 'Snowdonia from the Air', RCAHMW/SNP, 26-8
Davies, J.L. and Jones, R.H. 2006. Roman Camps in Wales and the Marches, University of Wales Press, Cardiff, 178-185.
Gresham, C.A. 1938, The Roman fort at Romen-y-mur, Archaeologia Cambrensis Volume XCIII (93), 192-211
Jarrett, M.G. 1962, Journal of the Merioneth Historical & Record Society, Volume IV, No. II (1962), 171-5
Jarrett, M. G., and Nash-Williams, V. E., 1969, The Roman Frontier in Wales, Second Edition, University of Wales Press,
Cardiff.
Simpson, G. 1962, Caerleon and the Roman Forts in Wales in the Second Century AD, Archaeologia Cambrensis, Volume CXI (111) , 142-4


John Wiles, RCAHMW, 11 February 2008, and Toby Driver, RCAHMW, 14 October 2008.