Baynard's Castle refers to buildings on two neighbouring sites in the City of London, between where Blackfriars station and St. Paul's Cathedral now stand. The first was a Norman fortification constructed by Ralph Baynard (fl. 1086), 1st feudal baron of Little Dunmow in Essex, and was demolished by King John in 1213. The second was a medieval palace built a short distance to the south-east and later extended, but mostly destroyed in the Great Fire of London in 1666. According to Sir Walter Besant, "There was no house in [London] more interesting than this".
The original castle was built at the point where the old Roman walls and River Fleet met the River Thames, just east of what is now Blackfriars Station. The north wall of the castle used as its foundation the Roman-era river wall from the 3rd century, distinguished by a tile-course of Roman brick. The Norman castle stood for over a century before being demolished by King John in 1213. It appears to have been rebuilt after the Barons' Revolt, but the site was sold in 1276 to form the precinct of the great Blackfriars' Monastery.