Pope Gregory IX was not a fan of cats. In fact, he hated them, so much that he decided he had to use his power to get rid of them. Being a pope this was quite easy, just accuse cats of being devil worshippers.
Gregory lived from 1145 to 1241 and was actually called Ugolino di Conti. When he became Pope at the age of 80, he decided Gregory was a better name suited for a pope. Gregory IX is famous for starting the Papal Inquisition, he issued what is known as the Decretales. These were a statement of laws that reissued many Catholic laws at the time. He was responsible for causing a whole new wave of the Catholic faith, where people spoke out against heretics and demanded they become Christians.
New Catholic laws were propped into place, ones that demanded justice for anyone who spoke against the will of the Pope and the church. And in this document there also happened to be a decree that condemned cats, notably black cats.
By Gregory’s decree, black cats were an instrument of Satan and they had to be destroyed. He single handedly condemned cats all over Europe, nearly overnight they were hunted down and killed completely.
The black plague arrived a century later and killed millions, a rough estimate is 200 million. Most historians have actually forgiven rats for causing the disease, noting it was airborne. But there is another theory: that at the time there were two diseases. One that spread airborne and one that was spread by rats. These historians argue is the explanation for why it was such a deadly time, how could one disease cause all this? There must have been two.
And if that were the case, the main cause of why there were so many rats about was that the cat population had larger been reduced to zero. All thanks to Pope Gregory IX.