In the early days of Christianity, the Romans accused Christians of cannibalism.
The early Christians (like contemporary Roman Catholics) believe in transubstantiation, the idea that the wine and bread of the eucharist actually turn into the blood and flesh of their deity, Jesus Christ. Since Jesus was also a man, it followed that the Christians were eating humans and drinking their blood in religious rites. This helped excuse Roman persecution of Christians (which officially ran from 64 c.e. under Nero to 313 c.e. and the Edict of Milan).
Thousands of Jews were murdered in Alexandria in 38 c.e. by people believing that the Jews were killing and eating Greeks, but it was actually the