In 1121 Robert, 1st Earl of Gloucester started work on St Mary's Church in the centre of the town, which was completed by 1137. A motte and bailey castle which gives its name to 'Castle Street' was built in 1139 during the Anarchy. The castle was demolished in 1154. The site is now home to Matalan. During the middle ages Luton is recorded as being home to six water mills. Mill Street, in the town centre, takes its name from one of them.