Boyce states that "no satisfactory evidence has yet been adduced to show that, before Zoroaster, the concept of a supreme god existed among the Iranians, or that among them Mithra – or any other divinity – ever enjoyed a separate cult of his or her own outside either their ancient or their Zoroastrian pantheons." However, she also says that although recent studies have minimized the Iranizing aspects of the self-consciously Persian religion "at least in the form which it attained under the Roman Empire", the name "Mithras" is enough to show "that this aspect is of some importance". She also says that "the Persian affiliation of the Mysteries is acknowledged in the earliest literary references to them."