The Roman origins of Cardiff Castle were discovered in 1888 when the 3rd Marquess of Bute decided to build a new tower and extend the grounds. The Roman remains were discovered in what was considered to be a solid earth bank. Rather than continue with his original plans Lord Bute decided to investigate and and reconstruct the Roman Fort.

The Roman walls were reconstructed in what was thought at the time to be an accurate way, with one exception, the addition of a gallery with in them. this was built for two reasons: to allow access to the substantial lower level of Roman remains and so that Lord Bute could still take his daily exercise even in bad weather.

The Roman wall galleries found a new role during World War II, when they were used as air-raid shelters by shoppers and cinema-goers from busy nearby streets during enemy action, accommodating nearly 2000 people.*

* Information from The Essential Cardiff Castle guidebook

In the Roman era, the coast line lay at the foot of the hill and has withdrawn over the centuries. The theatre therefore once stood near the sea front and was built exploiting the hill slope for the terraces, divided into four sectors by radial stairways. The site was restored to its current state at the end of the 1930s when a series of Medieval houses that had surrounded it in the meantime were eliminated. The theatre’s dimensions are considerable: the maximum diameter is 64 metres, whilst the terraces are 15 metres high and can seat around 6,000 spectators. Constructed between the 1st and 2nd century under the wishes of Tergeste’s Q. Petronius Modestus, State prosecutor for Emperor Trajan, the theatre fell into oblivion following the town’s dwindling importance. It was subsequently rediscovered in 1814 by archaeologists.