Complex sentence: During the Renaissance, it was accepted that Hermes Trismegistus was a contemporary of Moses, however after Casaubon's dating of the Hermetic writings as no earlier than the second or third century AD, the whole of Renaissance Hermeticism collapsed.
Split into simpler sentences: During the Renaissance, it was accepted that Hermes Trismegistus was a contemporary of Moses. However, after Casaubon's dating of the Hermetic writings, as being no earlier than the second or third century AD, the whole of Renaissance Hermeticism collapsed.