The cult of Mithraism was hugely popular in ancient military circles. According to its mythology, the Sun ordered Mithras, a young, handsome god, to slay a wild bull. As the animal died, it gave life, its blood causing wheat and other plants to grow.
Mithraic temples, known as Mithraeums, were almost always in underground locations or caves, reflecting the cult's belief that caverns represented the cosmos. In these Mithraeums, devotees underwent complex initiation rites, and ate bread and water to symbolise the body and blood of the bull. Sound familiar? The early Christians thought so too, and were fervently opposed to the cult.