Photograph of a carving on the wall of the Salt Tower at the Tower of London. The carving was made by Hew Draper, an innkeeper from Bristol accused of practising sorcery and imprisoned in the Salt Tower in 1561. Draper claimed that, although he had been interested in magic, he had destroyed all his magical books. During his imprisonment he carved a huge astrological sphere with Zodiacal signs on the wall of his cell, alongside the inscription: 'Hew Draper of Brystow made this sphere the 30 day of Maye anno 1561'. No record exists regarding Draper's fate.

The tower is part of the curtain wall built by Henry III in the late 1230s. It is situated on the south-eastern corner of the Tower of London and overlooks the River Thames. Its upper chamber contains examples of prisoners' graffiti, while the ground floor would have been used for storage. Prisoners in the tower include John Balliol, a Scottish king imprisoned here between 1296 and 1299, and Giovanni Battista Castiglione, Princess Elizabeth's tutor who transported letters for her during her time as a prisoner in the Tower.