The middle of the fourteenth century saw the arrival in Europe of a cataclysmic pandemic known forever as the Black Death, during which great swathes of the population were scythed down by the Grim Reaper. Those huddled together in squalid prisons in crowded towns were especially susceptible. They could even be exploited, as the example of Bedford shows. When the Black Death reached there on 23 May 1349, the mayor, Henry Arnold, summoned Johanne Warderare, the keeper of the town gaol, and told him that as he had ‘three sturdy vagrants in custody to die betimes at Gallows Corner, and four prisoners awaiting trial for felony before the Court of Pleas’, he should tell them that they should have ‘life and liberty’ if they agreed to ‘drive the death cart at the stated hours and dig a great pit in Bury Field and stand by to bury the dead’. They had nothing to lose, and they found ready employment as the town was devastated.

London in particular was an ideal setting for the spread of disease. Many people living in close proximity in cramped, filthy dwellings in cramped, filthy streets meant that every household was prey to fleas and vermin, and the transmission of infection from person to person was easy. While palaces and priories were not exempt, London prisons were incubators of disease. Newgate and Ludgate were situated near London's great open sewer, the ditch that ran by the Fleet prison. It was ten feet wide and deep enough to carry a boat laden with a tun of wine, but it was so choked with the effluence of eleven latrines and three sewers that no water from the river Fleet could flow around it. Smelly sludge, deep enough to drown in, surrounded the unhappy inmates.