It was built partly over the entrance to the courtyard of the great Blackfriars Mansion
(once, the lodging of the Prior of Blackfriars and later
owned by the Earl of Northumberland)
and has an interesting history. About 1554, this mansion was in the possession of Thomas Thirlby, Bishop of Ely, who sold it to his cousin William Blackwell, town clerk of London; at the latter's death in 1569, the property was inherited by his widow Mary, née Campion, a kinswoman of the famous martyr of the English Counter-Reformation, Edmund Campion; the deprived Catholic Bishop of Ely was given permission to lodge at Mistress Blackwell's house shortly before his death in 1570.
In 1585, Widow Blackwell was accused of recusancy, but she was able to produce documents certifying that she had attended Anglican services. About 1586, a Government informer reported his suspicions regarding Blackfrairs House: 'Now there dwells in it one that is a very inconformable man to her Majesty's proceedings. It has sundry backdoors and bye-ways, and many secret vaults and corners. It has been in time past suspected, and searched for Papists, but no good done for want of knowledge of the backdoors and bye-ways of the dark corners.'
Whether the suggested daylight search was actually carried out is unknown. In 1589, a recusant from Norfolk, Edward Walpole, was licensed to visit Anne Bacon (Widow Blackwell's daughter) there.
About this time, the Blackfriars mansion came into the possession of Henry, ninth Earl of Northumberland, himself strongly suspected of papistry,
and in 1590, the Gatehouse passed into the hands of Anne Bacon's son Mathias. Bacon's second tenant there was a Catholic named John Fortescue of Lordington, Sussex (his father, Sir Anthony Fortescue, was concerned in a conspiracy against Elizabeth in 1562; his mother was one of the Catholic Poles, related to Cardinal Pole)" (Mutschmann and Wentersdorf 136, 137). (See also: Fortescue.)