Complex sentence: Taken together, the "Vatican Mythographers" provided a source-book for the myths of Greeks and Romans and their iconography through the Middle Ages and the Renaissance; their texts were copied in manuscripts as late as the fifteenth century.
Split into simpler sentences: Taken together, the "Vatican Mythographers" provided a source-book for the myths of Greeks and Romans and their iconography through the Middle Ages and the Renaissance. The texts were being copied in manuscripts as late as the fifteenth century.