St John's Abbey, also called Colchester Abbey, was a Benedictine monastic institution in Colchester, Essex, founded in 1095. It was dissolved in 1539. Most of the abbey buildings were subsequently demolished to construct a large private house on the site, which was itself destroyed in fighting during the 1648 siege of Colchester. The only substantial remnant is the elaborate gatehouse, while the foundations of the abbey church were only rediscovered in 2010.