This will be a representation of Mithra(s) sacrificing the astral bull, a tauroctony. No information given.

From the Enc. Brittanica: According to myth, Mithra was born, bearing a torch and armed with a knife, beside a sacred stream and under a sacred tree, a child of the earth itself. He soon rode, and later killed, the life-giving cosmic bull, whose blood fertilizes all vegetation. Mithra's slaying of the bull was a popular subject of Hellenic art and became the prototype for a bull-slaying ritual of fertility in the Mithraic cult.