Long a commercial, cultural and educational centre, Lancaster gives Lancashire its name. The House of Lancaster was a branch of the English royal family, whilst the Duchy of Lancaster holds large estates on behalf of Elizabeth II, who is also the Duke of Lancaster.
The city's name, first recorded in the Domesday Book in 1086 as Loncastre, where "Lon" refers to the River Lune, and "castre", from the Old English cæster and Latin castrum for "fort", refers to the Roman fort which stood at the site.
A Roman fort was built by the end of the 1st century AD on the hill where Lancaster Castle now stands, and possibly as early as the 60s, based on Roman coin evidence. The coin evidence also suggests that the fort was not continuously inhabited in those early years. It was rebuilt in stone around AD 102. The fort's name is known only in an abbreviated form; the only evidence is a Roman milestone found 4 miles outside Lancaster, with an inscription ending L MP IIII, meaning "from L— 4 miles".
Roman baths were discovered in 1812 and can be seen near the junction of Bridge Lane and Church Street. There was presumably a bath-house belonging to the 4th-century fort. The Roman baths incorporated a reused inscription of the Gallic Emperor Postumus, dating from AD 262–266.