The Constantinian Shift was when the Christian religion went from being a persecuted group of people to being the official religion of the Roman Empire under Emperor Constantine the Great. Constantine declared that Christians were free to practise their religion and he even supported their churches and priests with public money. This was a big change because before that, Christians had been persecuted and sometimes even killed for their beliefs. It changed the face of Christianity as it helped it to spread more widely and gain more followers.