Constantine the Great (280? – 337AD). In 312 AD, he received, he believed, the help of the Christian God at a crucial battle, thus becoming ruler of the Roman empire's western half. A year later, in the Edict of Milan, he legalized Christianity. By 324 he ruled the Empire's eastern half as well. In 326 his immensely popular, 72-year-old mother Helena made a journey to the Holy Land, establishing the trend of Christian pilgrimage and – through her discovery of the true cross – founding the science of archaeology. With her son's support, she erected churches.

 

In 330, having built up the ancient city of Byzantium as his new capital, Constantine renamed it Constantinople and dedicated it to the God of the Christians, whom he seems to have confused with himself. He delayed becoming a Christian till his last illness: few Christians then believed in post-baptismal forgiveness for serious sins. .