This religion's main act of sacrifice was a tauroctony or slaying of a bull, which took place in a namesake cave.
Ernest Renan famously remarked that if Christianity had been halted by some mortal illness, then this would have been the dominant religion in the world. Initiation into this religion involved tying one's hands with chicken intestines then hopping over pools of water. In this religion, a "courier of the sun" called a heliodrome and a lion symbolized by the planet Jupiter are two of its seven grades. This henotheistic religion venerated a deity that was born from a rock with dagger in hand, possibly sometime around Christmas. This religion's main act of sacrifice was a tauroctony or slaying of a bull, which took place in a namesake cave. For 10 points, identify this mystery religion of the Roman Empire, named for a Persian deity.
Ernest Renan famously remarked that if Christianity had been halted by some mortal illness, then this would have been the dominant religion in the world.
mithrasism [or even Mithraism or worshipping Mithras]