The Roman fort near Pennal in Gwynedd is situated along the crest of the ridge running north-east from Cefn-Caer Farm. The fort measures approximately 550 feet from north-east to south-west, by about 425 feet transversely (c.168 x 130 m), and therefore covers an area of around 5 and one-third acres (c.2.17 ha). The fort is protected by two ditches on the south-west side and around the southern corner-angle, possibly by three ditches on the south-east and north-east sides. Aerial photography has revealed the line of the stone wall of the fort on the NE, SE and SW sides, also the foundations of a stone building in the centre of the fort, the principia, measuring about 90 feet (c. m) square. Aerial photography has also detected signs of extramural activity on the slopes between the fort's defenses and the marshy ground to the south-west (JRS 1953 pp.86/7, 1977 pp.151/2).
The foundation date of the Pennal Roman fort is debatable. It is possible that the Dyfi valley was occupied during the tenure of governor Quintus Veranius c.A.D.57/58, and the discovery of a couple of central-Gaulish lead-glazed bottles within a destruction layer suggest that occupation possibly continued until the early-70's (Webster p.114).
A magnetometry survey was conducted in 2000 using a fluxgate gradiometer which revealed details of the fort and its defenses "set in a wider landscape containing both military and civilian features" (Britannia 2001). The survey confirmed the line of the road running eastwards from the fort which was previously known only from crop marks in aerial photographs and also showed ribbon development to either side of both roads leading from the main gates of the fort extending for over 220 yards (200m) beyond the defenses. Various features were identified in the immediate environs of the fort, including a bath-house, a circular tomb or perhaps a shrine, what appears to be a ansion or imperial posting station, also traces of an adjacent parade-ground. There were signs of extensive development along the lines of both roads which was interpreted by the surveyors as a settlement in the form of vicus, complete with a shrine, bath-house and imperial hostel, also a complex of buildings of "unknown function." All this was learned without so much as lifting a spade. Ah! The wonders of modern archaeology!
The above - and much more on this period in history can be found on Roman Britain
Detailed topographical surveys have been produced for the visible remains of most of the surviving auxiliary forts of Gwynedd and several have been excavated. In most cases the work only extended as far as the edge of the visible earthworks. A great deal of evidence has accumulated, both in Wales and further afield demonstrating that Roman forts should not be seen as standing alone in the landscape but instead viewed as the centre of a wider area of both military and civilian activity. Evidence from crop marks, rescue excavation and chance finds has revealed the presence of extramural remains at several forts in Gwynedd but the evidence was general fragmentary. The Cadw funded Roman Fort Environs Project aims to gain information about the environs of the forts using fluxgate gradiometer survey. Gwynedd Archaeological Trust has so far carried out surveys at the following sites: Cefn Caer (Pennal), Caer Gai (Llanuwchllyn), Pen Llystyn (Bryncir), Caer Llugwy (Capel Curig) and Canovium (Caerhun).
The surveys have produced a wealth of new information about the forts and their environs. The results from the previously largely unexplored fort at Cefn Caer, Pennal are particularly informative showing details of the fort and its defenses set in a wider landscape containing both military and civilian features including a vicus alongside the road to the north east of the fort (see figure).
Also to be seen at Cefn Caer is a wonderful display of Roman vases and other historical artifacts which have been found on the land.