I have studied this many times.
Black cats were feared by early Christians and associated with witches. Black cats are hard to see at night, and cats are typically nocturnal. As such people became fearful of them, thinking witches were turning into cats at night to sneak about. Sadly cats were also linked with the devil since you will note that cats are aloof and not nearly as personable as a dog, particularly when we think of those early days when cats were mostly feral in the streets and not often kept as pets.
Cats were even blamed for spreading the plague, but in truth this was fleas on rats. But ignorance caused many religious people to think that cats were used by witches and/or the devil to spread teh plague.
For these reasons cats were killed in massive numbers, often thrown into the fires or thrown off buildings. Not just black cats, but all cats. Although black cats in specific were feared the most.
It was not until the Welsh King made cat killing illegal that the horrific cat slaughter was slowed in the UK. Although when the Salem witch hunts were active in the USA cats were killed by being thrown into the fires then too, again because people thought witches could turn into cats to escape the witch hunts. Again black cats were feared most, because they were harder to see at night, but all cats were feared.
Interesting to note, we are told now that it was pagans who practiced cat sacrifice on Halloween but this is not true. Although one group of Scots did kill cats for some weird devil worship ceremony witches and pagans who kept cats as pets loved them and did nothing to harm them. It was early Christians who engaged in the massive killing of cats and history has recorded this.



