Any British town ending in ‘chester’ is highly likely to have been a substantial Roman settlement and big enough to have had an amphitheatre. Whilst subsequent history is likely to have obliterated anything remaining in Manchester, nothing has yet been found in Exeter (Exchester), Uttoxeter or Colchester (although there are claims that the latter site is known, I’ve yet to see any evidence or accounts of excavations). The principle is however firmly supported by Chichester, Chester, Silchester and of course Dorchester.

There is plenty of evidence of Roman use of topography in the construction of amphitheatres but repurposing an existing structure is quite rare. This is however what happened at Dorchester. The site is known as Maumbury Rings and started as a Neolithic Henge comprising a circular earthwork, 85 metres in diameter, with a single bank and an entrance to the north east. It was modified during the Roman period when it was adapted for use as an amphitheatre.  

The banks were lowered by around 3 metres, with the material used to reinforce them. The interior was modified with an oval, level arena floor, and seating was cut into the banking which was revetted with either chalk or timber.  

The southern end was modified in 1642/3 to provide a defensive gun emplacement by the parliamentarians during the Civil War. 

In the late 17th and early 18th centuries the arena was still used as a place of public execution and saw 80 participants of the Monmouth Rebellion dispatched on the order of the notorious Judge Jeffreys as well as, In 1705, Mary Channing, a nineteen-year-old woman found guilty of poisoning her husband. This got a mention in Hardy’s The Mayor of Casterbridge (1886). 

In 1846, the proposed alignment of the Southampton and Dorchester Railway was amended in order to avoid the site. The amphitheatre is open as a public amenity and well worth a visit.