A major turning point in western history occurred when the Roman Emperor Constantine converted to Christianity in 312 CE.
Whether Constantine's conversion was sincere or politically motivated (or a combination of the two), historians can only speculate. But the result was the end of persecution of Christians and the beginning of Christendom.
In 313 Constantine issued the "Edict of Milan," which granted official toleration of Christianity and other religions. He ordered that Sunday be granted the same legal rights as pagan feasts and that feasts in memory of Christian martyrs be recognized.
Constantine also outlawed gladiatorial shows (although they persisted until the 5th century) and forbade Jews to stone to death other Jews who converted to Christianity.
Contrary to popular belief, however, Constantine did not make Christianity the official religion of the empire. This was accomplished by Emperor Theodosius in 380. Constantine's program was one of toleration only, and he continued to support both Christianity and paganism.
In 314, the cross appeared on Constantine's coins, but so did the figures of Sol Invictus and Mars Convervator. He raised his children as Christians and secured Christian clergy as personal advisors, but retained the title pontifex maximus, the chief priest of the state cult, until his death.