The Chapel of St Peter-on-the-Wall, Bradwell-on-Sea, Essex, is a Grade I listed building and among the oldest largely intact Christian churches in England; it is the 19th oldest building in the country and is still in regular use. It dates from between 660–662.
The Chapel is said to be that of "Ythanceaster" (Bede, Historia Ecclesiastica 3.22), originally constructed as an Anglo-Celtic church for the East Saxons in 654 by Cedd astride the ruins of the abandoned Roman fort of Othona. The current structure was most likely built around 660–662, incorporating the Roman bricks and stones. Cedd travelled south from Lindisfarne to spread Christianity at the behest of Sigeberht the Good, then King of the East Saxons, in 653 and returned the next year having been ordained as a bishop in order to build the Chapel, and probably others too. Following the death of Cedd in October 664 from plague, the Chapel became part of the Diocese of London.
No further record exists of the Chapel's use until 1442 when the local clergy reported to the Bishop of London that it had been expanded slightly, with a small tower above the porch with a bell in it. However, they did not know of its origins and it was unusable, having been burnt. It was repaired and returned to regular use alongside the parish church in Bradwell-on-Sea until at least the Tudor period (16th century) before falling into disuse as a church again and being used as a barn—the position of the wide barn doorway, now filled in, can be seen on the south side of the nave.
In 1920, it was restored and reconsecrated as a chapel; it achieved Grade I listed status in 1959. The Chapel belongs to Chelmsford Cathedral and is looked after by the parish church of St Thomas. A public service is held there every Thursday at 9 am. Summer evening services are held there in July and August from 6:30pm. The parish also have other services at Easter and Christmas as well as other times of the year. The Othona Community, located five minutes walk away, generally uses the Chapel once a day in the summer for its short, informal acts of worship. Founded in 1946 by Norman Motley, rector of St Michael, Cornhill, 1956-1980, this Christian-based community is open to people of all faiths and none.