Thorney Island was the eyot (or small island) on the Thames, upstream of medieval London, where Westminster Abbey and the Palace of Westminster (commonly known today as the Houses of Parliament) were built. It was formed by rivulets of the River Tyburn, which entered the Thames nearby. In Roman times, and presumably before, Thorney Island may have been part of a natural ford where Watling Street crossed the Thames, of particular importance before the construction of London Bridge.
Thorney is described in a purported 8th century charter of King Offa of Mercia, which is kept in the Abbey muniments, as a "terrible place". In the Spring of 893, Edward the Elder, son of Alfred the Great, forced invading Vikings to take refuge on Thorney Island. Despite hardships and more Viking raids over the following centuries, the monks tamed the island until by the time of Edward the Confessor it was "A delightful place, surrounded by fertile land and green fields". The abbey's College Garden survives, a thousand years later, and may be the oldest garden in England.
Since the Middle Ages, the level of the land has risen, the rivulets have been built over, and the Thames has been embanked, so that there is now no visible Thorney Island. The name is kept only by Thorney Street, at the back of the MI5 Security Service building; but a local heritage organisation established by June Stubbs in 1976 took the name The Thorney Island Society.