Constantine the Great was a fourth century Roman emperor who reigned from 306-337 AD. In 306 Constantine ruled only over the far western portion of the Roman Empire which had been divided into four sections by Diocletian. Over the next 17 years he would slowly consolidate his power, becoming sole emperor in 323.
The Da Vinci Code is at least accurate when it states the he was a signficant figure in the history of the Church. His relocation of the capital from Rome to Constantinople had enormous consequences on Western European history and the rise of the Roman Catholic Church as a political force.
More significantly, however, was his conversion to Christianity in 312 at the Battle of the Milvian Bridge outside Rome. From this point in time Constantine began to favour Christianity and although it was another fifty years before Christianity became the official religion of the empire this represented a significant turning point in Christian history. For the first time Christianity had legal status in the Roman Empire.
The obvious imperial patronage made Christianity more appealing to many in the empire (as did the fact that persecutions ceased) and paved the way for the marriage of Church and State which would dominate for the next millennium and a half.
While the significance of this is outside the scope of this booklet it is useful to note that religion and politics were intertwined in the ancient world. Constantine's support of religion was not new or surprising only his choice of religions.
With this brief introduction we are ready to examine the claims of The Da Vinci Code.