Of course the oldest empires in the world were religious empires, centring upon the worship of a god or of a god-king. Alexander was treated as a divinity and the Cæsars were gods in so much as they had altars and temples devoted to them and the offering of incense was made a test of loyalty to the Roman state. But these older religions were essentially religions of act and fact. They did not invade the mind. If a man offered his sacrifice and bowed to the god, he was left not only to think but to say practically whatever he liked about the affair. But the new sort of religions that had come into the world, and particularly Christianity, turned inward. These new faiths demanded not simply conformity but understanding belief. Naturally fierce controversy ensued upon the exact meaning of the things believed. These new religions were creed religions. The world was confronted with a new word, Orthodoxy, and with a stern resolve to keep not only acts but speech and private thought within the limits of a set teaching. For to hold a wrong opinion, much more to convey it to other people, was no longer regarded as an intellectual defect but a moral fault that might condemn a soul to everlasting destruction. THE RAVENNA PANEL, DEPICTING JUSTINIAN AND HIS COURT THE RAVENNA PANEL, DEPICTING JUSTINIAN AND HIS COURT _Photo: Alinari_ THE ROCK HEWN TEMPLE AT PETRA THE ROCK HEWN TEMPLE AT PETRA _Photo: Underwood & Underwood_ Both Ardashir I who founded the Sassanid dynasty in the third century A.D., and Constantine the Great who reconstructed the Roman Empire in the fourth, turned to religious organizations for help, because in these organizations they saw a new means of using and controlling the wills of men. And already before the end of the fourth century both empires were persecuting free talk and religious innovation. In Persia Ardashir found the ancient Persian religion of Zoroaster (or Zarathushtra) with its priests and temples and a sacred fire that burnt upon its altars, ready for his purpose as a state religion. Before the end of the third century Zoroastrianism was persecuting Christianity, and in 277 A.D. Mani, the founder of a new faith, the Manichæans, was crucified and his body flayed. Constantinople, on its side, was busy hunting out Christian heresies. Manichæan ideas infected Christianity and had to be fought with the fiercest methods; in return ideas from Christianity affected the purity of the Zoroastrian doctrine. All ideas became suspect. Science, which demands before all things the free action of an untroubled mind, suffered a complete eclipse throughout this phase of intolerance.