Caerleon often referred to as the 'city of the legions' was the site of the Roman Fortress of Isca. It was the permanent home of the Legio II Augusta, named after the emperor Augustus who had raised or possibly reformed the second legion. The site was first occupied cAD75 by Sextus Julius Frontinus who had been instructed by Emperor Vespasian to pacify the Welsh and the site he chose provided an easily defendable area with good access down the Usk estuary, for essential supplies by sea. The surviving areas of the site that visitors see today comprise of four main sections: the Baths, the Amphitheatre, the Barracks and defences, and give a good overall picture of how Caerleon Roman Fortress may have looked during its years of occupation.
Caerleon Roman Fortress covers some 50 acres, is rectangular in shape with four entrances, one in each side. The perimeter was protected by a deep ditch, the contents of which were used to build an internal earthen bank, and would have been topped with a timber palisade and rampart. The timber defence was later replaced in stone and a large section of this wall can still be seen, to a height of some 12ft (3.6m) in places, in the south-eastern corner of the modern town. In the centre of the modern town can be found the remains of the bath buildings. The baths would have been originally much bigger than the remains currently on show and would have comprised of the main bath complex with its main bathing halls, the frigidaruim, tepidarium and caldarium. Adjoining this would have been a huge exercise hall known as the basilica, and a colonnade would have formed an outer courtyard area which contained an outdoor pool called a natatio, fed from an elaborate fountain house. The only surviving elements now preserved under a modern cover building are the natatio, the first of the bathing halls, the frigidaruim and the apodyteruim which was a heated changing room, the underfloor hypocaust of which can still be seen.
To the south of the site, outside of the main fortress defences can be found the most famous monument in Caerleon, the Amphitheatre. This was Oval in shape and was comprised of a lower story built of well-buttressed stone and an upper seating level of timber construction. There were eight entrances to the arena, two main entrances used for opening processions, and six lesser entrances for spectators. In its heyday it would have seated in the region of 6,000 people and would have been the scene of many gladitorial games against men and beasts. Dr Mortimer Wheeler extensively excavated the remains of the Amphitheatre in 1926 and they remain some of the best preserved in Britain.
The final area of remains and some of the most impressive are the four surviving barrack blocks in what is now Prysg Field. These are the only surviving legionary barracks in Europe and give the visitor a good idea of the size of Caerleon Roman Fortress, as at one time there would have been 60 of these barrack blocks. Fortunately the Centurions quarters have also survived in the first block and give a good idea of how his senior position afforded him much grander accommodation. The barracks were excavated in 1927 by Dr Nash-Williams and include several of the circular ovens and the latrine block, situated along the outer defence wall. Many of the artefacts discovered during the various excavations can be seen in the towns Roman Legionary Museum which is also well worth the visit.