The Right bank from Old Culham Bridge to half a mile above Abingdon Lock is Andersey Island - bounded by the Swift Ditch backwater weir stream
and the main channel of the river.
The island of Andersey was the site of a royal residence from an early period.
In his great charter of 993, Aethelred II refers to the 'royal building' on the 'estate called Abingdon'.
Shortly before the Conquest, Andersey was granted by Abingdon Abbey to a wealthy secular priest named Blacheman, who built a church dedicated to St Andrew, and an elaborate house built around a cloister.
After the Conquest, Blacheman, who had attached his fortunes to those of Gytha, Earl Godwin's widow, and fled the country after the siege of Exeter.
His estates were siezed by King William, who converted Andersey to a royal residence.
However, in 1101-2 the buildings were ruinous, and Henry I granted permission to the Abbot of Abingdon to demolish the buildings and use the materials to rebuild his monastery.
According to Leland the buildings were fortified, and in C16 the site was still known as the 'Castle of the Rhae'.
He says the site was almost in the middle, between the old and new bottom of the Isis, and that an old barn stood on the site. (PastScape)
After the Conquest both William I and William II used to stay at the royal hunting lodge on Andersey.
The Conqueror in particular delighted in the island's green meadows and recuperated there from blood-letting, (Chron. Abingdon, ii. 49) but Henry I was persuaded by Queen Maud to return the island to Abingdon and to allow the abbot to use the lead from the many houses on the island for the roof of the abbey church.
It appears from the chronicler's account that the stone buildings on the island were already in decay, (Ibid. 50–51) but local memory of them was still strong when Leland visited Culham.
He says that there was once a 'fortres or pile lyke a castle in Andersey' and that it lay almost exactly between the old and new courses of the Thames. (Leland, Itin. v. 76) (VCH)