Strictly speaking, Yeoman Warders are responsible for guarding any prisoners held at the Tower of London and for protecting the Crown Jewels. In practice, however, the Yeoman Warders act as tour guides and are a tourist attraction in and of themselves, something that they acknowledge. This Yeoman Warder is describing Traitor's Gate behind him. Political prisoners, including Queen Anne Boleyn, were frequently delivered to the Tower via barge on the River Thames and brought in to the Tower through this gate, which sits at water level on the river.