The earthworks of the Roman fort are still prominent in the village today and first became the subject of enquiry in the late eighteenth century when they were described by Thomas Pennant. In 1804 Sir Richard Colt-Hoare measured the earthworks and recorded several finds that had eroded out of the river bank, and further work was conducted by Revd. David Davies in 1854-5. The first modern excavation was undertaken by R.C. Bosanquet in 1909, and these were followed by a series of sporadic excavations through the 1960s, 1980s and 1990s.

The fort is located in a central position in the Roman military system controlling mid Wales, with roads leading east, north, north-west and west, with a further, as yet unlocated, road to the south towards Castell Collen. It measures 188m by 177m, enclosing an area of 3.2ha. It's earliest phase appears to be very early Flavian (c. AD 70), with subsequent Trajanic / Hadrianic (c. AD 120) and Hadrianic / Antonine (c. AD 140) phases, but the site appears to go out of military use in the early third century. An annex was added on the northern side in the early second century, and there was an extensive vicus on the south and east sides. This vicus had a developed series of streets, timber buildings, and the possible temenos of a temple was identified during excavations in the 1990s. A bathhouse discovered in 1854 lay to the south of the fort but what remains of this now lie beneath the railway.

Sources: Davies in Archaeologia Cambrensis third series III (1857), 151-72 - excavations in 1854, includes discovery of bathhouse
Pryce in Montgomeryshire Collections 42.1 (1932), 17-67 - excavations of 1909
42.2 (1932), 142-7
46.1 (1939), 67-90 - excavations of 1909
Jones in the Bulletin of the Board of Celtic Studies 19.2 (1961), 177-92 - review
Daniels and others in Montgomeryshire Collections 59 (1966), 112-5 - excavations in 1966
60 (1968), 64-6 - excavations in 1967
61 (1970), 37-42 - excavations in 1968
Jarrett 'The Roman Frontier in Wales' second edition (1969), 66-70 - review
Stephens in Montgomeryshire Collections 74 (1986), 32-7 - stamped tile
Britnell 'Caersws Vicus' British Archaeological Reports British series 205 (1989) - excavations in 1985-6
Jones in Montgomeryshire Collections 81 (1993), 15-96 - excavations in 1984-92
84 (1996), 1-36 - excavations in 1989-93
Milne in Archaeology in Wales 41 (2001), 139 - watching brief
Jones & Hankinson in Archaeology in Wales 42 (2002), 120 - small scale work

J.Wiles, RCAHMW, 09 August 2002.