Truro (; ) is a cathedral city and civil parish in Cornwall, England. It is Cornwall's county town, sole city and centre for administration, leisure and retail trading. Its population was 18,766 in the 2011 census. People of Truro can be called Truronians. It grew as a trade centre through its port and as a stannary town for tin mining. It became mainland Britain's southernmost city in 1876, with the founding of the Diocese of Truro. Sights include the Royal Cornwall Museum, Truro Cathedral (completed 1910), the Hall for Cornwall and Cornwall's Courts of Justice. Toponymy Truro's name may derive from the Cornish tri-veru meaning "three rivers", but authorities such as the Oxford Dictionary of English Place Names have doubts about the "tru" meaning "three". An expert on Cornish place-names, Oliver Padel, in A Popular Dictionary of Cornish Place-names, called the "three rivers" meaning "possible". Alternatively the name may come from tre-uro or similar, i. e. settlement on the river Uro. History A castle was built in the 12th century by Richard de Luci, Chief Justice of England in the reign of Henry II, who for court services was granted land in Cornwall, including the area round the confluence of the two rivers. The town grew below the castle and gained borough status from further economic activity. The castle has long disappeared. Richard de Lucy fought in Cornwall under Count Alan of Brittany after leaving Falaise late in 1138. The small adulterine castle at Truro, Cornwall, originally the parish of Kenwyn, later known as "Castellum de Guelon", was probably built by him in 1139–1140. He styled himself "Richard de Lucy, de Trivereu". The castle passed to Reginald FitzRoy, an illegitimate son of Henry I, when he was invested by King Stephen as the first Earl of Cornwall. Reginald married Mabel FitzRichard, daughter of William FitzRichard, a major landholder in Cornwall. The -diameter castle was in ruins by 1270 and the motte was levelled in 1840. Today Truro Crown Court stands on the site. In a charter of about 1170, Reginald FitzRoy confirmed to Truro's burgesses the privileges granted by Richard de Lucy. Richard held ten knights' fees in Cornwall before 1135. At his death the county still accounted for a third of his considerable total holding. By the early 14th century Truro was a major port, due to an inland location away from invaders, to prosperity from the fishing industry,