VATICAN CITY - For Vatican historians, the roots of a Christian idea of religious liberty go way back: in fact, back 1,700 years to the Emperor Constantine's victory on Rome's Milvian Bridge and to his conversion.

At a Vatican conference in late April marking the anniversary, the head of the Pontifical Committee for Historical Sciences said Constantine's victory in 312 under the sign of the cross was "the foundation of a new world" marked by religious freedom for Christians and separation between church and state.