Etsi ecclesia Christi is a papal bull issued by Pope Nicholas V on 30 September 1453 in response to the fall of Constantinople to the Ottoman Empire.[1]
Nicholas declared that the capture of Constantinople by the Ottomans was the latest in a long line of attacks on Christendom from Islam, whose followers had already conquered the East, Egypt and North Africa.[1] He further claimed that these were the fulfilment of John's prophecies in the Book of Revelation and he called the Ottoman Sultan Mehmed II the "second Mohammed",[1] and a forerunner of the Anti-Christ.[2] Nicholas called on Christian rulers to defend Christendom with their lives and their money and he granted indulgences to those who, for six months, took part in this crusade.[3]