The Saxons may have given Colchester its modern name, which derives from Colneceaster, meaning ‘Fortress on the Colne'. Only one of their buildings, the tower of Holy Trinity Church still stands. This dates from about 1000 and is the earliest surviving medieval building in Colchester which the brick and tile of the ruined Roman town can be seen out to new use.
The victory of William the Conqueror at the Battle of Hastings in 1066 brought Anglo-Saxon England to and abrupt end. The Normans found a busy port and market town at Colchester, and chose it as the site for one of the first stone castles in England. Construction on Colchester Castle began within ten years of the conquest, pre-dating both the Tower of London and Norwich Castle.
The massive foundations of the ruined Temple of Claudius formed a convenient base for the castle keep, which is consequently the largest ever built by the Normans. Its purpose was both to contril the town and surrounding area and to act as a defence against seaborne invasion from Scandinavia. In practice it saw military action only once, in 1216 when King John besieged the castle and recaptured it from French mercenary troops sent to aid his rebellious barons.
The long entry for Colchester in the Doomsday Book catalogues a small but wealthy town. A new port was established at the Hythe before 1200, thriving on international trade, and in 1189 the town received the first Royal Charter, from King Richard I. This gave wealthier citizens various rights to manage local affairs, including markets, the Colne fisheries and judicial arrangements. These privileges were confirmed and extended by successive charters throughout the Medieval period.
Medieval Colchester had a number of religious foundations, including St. Botolph's Priory, the first Augustinian house in England, and St John's Abbey. Today the impressive ruins of the great church at St Botolph's only hint at the scale of the medieval priory, while at St John's Abbey some long seciotns of the precinct wall and the later Tudor gatehouse survive.
In 1348 at least a quarter of Colchester's population died of the plague as the Black Death decimated Western Europe. The town not only survived the crisis but soon experienced a new golden age as trade recovered and the local cloth industry boomed.