Dorchester (/ˈdɔːrtʃɛstər/ DOR-ches-tər) is the county town of Dorset, England. It is situated between Poole and Bridport on the A35 trunk route. A historic market town, Dorchester is on the banks of the River Frome to the south of the Dorset Downs and north of the South Dorset Ridgeway that separates the area from Weymouth, 7 miles (11 km) to the south. The civil parish includes the experimental community of Poundbury and the suburb of Fordington.
The area around the town was first settled in prehistoric times. The Romans established a garrison there after defeating the Durotriges tribe, calling the settlement that grew up nearby Durnovaria; they built an aqueduct to supply water and an amphitheatre on an ancient British earthwork. During the medieval period Dorchester became an important commercial and political centre. It was the site of the "Bloody Assizes" presided over by Judge Jeffreys after the Monmouth Rebellion, and later the trial of the Tolpuddle Martyrs. As well as having many listed buildings, a number of notable people have been associated with the town. It was for many years the home and inspiration of the author Thomas Hardy, whose novel The Mayor of Casterbridge uses a fictionalised Dorchester as its setting.