St Anthony’s Fire, also known as ergotism, was a disease, common in Medieval times, caused by eating – improperly-stored – cereals contaminated by an alkaloid-secreting fungus. Its symptoms included a rash, fever and delirium (sometimes taken as evidence of bewitchment).
St Anthony’s Hospital, or the Hospital of St Antoine de Viennois, specialising in the treatment of the disease, was founded on the site of a former synagogue on Threadneedle Street in 1242. It was later expanded so as to incorporate, in 1429, a hospice; in 1440, a school, where Thomas More (1478-1535) studied; and, in 1550, a chapel, where Protestant Huguenots, fleeing religious persecution in Catholic France, worshipped. It was burned down in the Great Fire of 1666, and subsequently rebuilt, only to be demolished in 1840.