Pope Innocent III

Seán Manchester (from his writings) on Pope Innocent III:

Innocent III (Pope from 8 January 1198 until his death on 16 July 1216) sanctioned the publication of a treatise on how to make the discovery of vampires and thus elimate them. The authorative teaching of the Fourth Lateran Council under Innocent III in 1215 dogmatically lays down:"Diabolus enim et alii daemones a Deo quidem natura creati sunt boni, sed ipsi per se facti mali." A massive gathering of fifteen hundred prelates listened to his decrees and passed them. Innocent III ruled the world in tranquil majesty for close on twenty years. He called for Christian crusades against Muslims in Spain and the Holy Land and against heretics in southern France.

Copies of the treatise held in the Vampire Research Society archive are in Latin. I am unaware of an English translation. Though extracts might possibly be found in some academic works on the topic by other authors.

Bear in mind that the Slavic word "vampire" was not in use until a much later century, so reports referred to incubi, succubi, revenants and such creatures of the night that nevertheless meet with vampire criteria.