10/28/2012 05:55 pm ET | Updated Dec 28, 2012

On a Bridge Near Rome, an Empire Converts to Christianity

The Ponte Milvio is Rome's oldest bridge. Its first stone-built ancestor dates back to 115 BC when it was outside the city limits. Nowadays the bridge, which carries the Via Flaminia cross the Tiber in the northern end of Rome, has become a sort of Lovers' Lane. Inspired by Federico Moccia's Ho voglia di te (I want you) couples come here to place padlocks testifying to their love. There are now a lot of them. Seventeen hundred years ago, on Tuesday, October 28, the scene was very different. That day the bridge featured in a battle that changed the course of history.

There aren't many battles that changed history, and making this sort of claim for any battle may seem pretty melodramatic. But the events of October 28, 312 were melodramatic. On that day the Roman emperor Constantine defeated his rival emperor Maxentius, and in doing so found proof that he had made the right decision a few months earlier. That decision was to become a Christian; in the next two decades Constantine encouraged millions of his subjects to become Christians as well. By the time of his death on May 22, 337 Christianity was firmly established as the dominant religion in the Roman Empire. Just a few years before he converted, Christians were victims of a savage persecution, and it seemed that the best they could hope for was that they once again be a tolerated minority within the empire.

For all of its profound significance -- and Constantine made it clear to everyone that he won because of guidance from his god, whom referred to as the Highest God (a sign that he had some trouble understanding the concept that there could be only one God) -- the battle itself was neither long nor hard fought. That's because Constantine had already undermined Maxentius through a brilliant campaign in northern Italy. Although Maxentius' subordinates held the area with experienced armies, Constantine crushed them in a lightning fast operation. He knew how to bring immense psychological pressure to bear on his opponents, forcing them into mistakes -- the sort of thing that Robert E. Lee did so masterfully during our own Civil War -- and how to reach out to leaders on the other side. Constantine knew that once he won, he would have to govern, and that he needed the skills of the people who were running Maxentius' part of the empire. Many of Maxentius' people moved into the upper echelons of Constantine's regime immediately after the Battle of the Milvian Bridge, and it's clear Constantine was negotiating to bring them over to his side during the campaign.

After losing northern Italy, Maxentius was in trouble. Immensely superstitious, he moved out of the palace in the days before the battle to the house where he'd lived before becoming emperor, and placed the man who had held the high office of Prefect on the day he had seized the throne on October 28, 307 back in office as a sort of good luck charm. Recently Italian archaeologists excavating Maxentius' palace on the Palatine Hill found some of the imperial gear that he left behind when he moved out. On the morning of October 28, 312, he drew up his army with the Tiber and the bridge at his back. Constantine must have recognized the act of a desperate man trying to force his men to "do or die." Maxentius' own people seem to have recognized the same thing and the battle ended when Constantine ordered his men to advance. Maxentius' army fell apart and Maxentius drowned in the Tiber when his horse fell off the Milvian Bridge. Visitors to Rome can see this scene today on the arch that was erected next to the Colosseum in Constantine's honor by the Roman Senate in 315.

People looking at the arch will not find any mention of the famous story that Constantine converted to Christianity because he saw the sign of a cross in the sky with the words "In this Sign Conquer." The reason for this is simple--the story was invented years after the event and after the arch was dedicated. At the time, Constantine simply told people that he had had a personal encounter with a God who had shown him the path to victory. It was a God he had seen in "the watch post" of heaven as he sought answers to the question of how he could be a better, more successful ruler. After the Battle of the Milvian Bridge, Constantine knew that he'd found his God and the Roman Empire soon joined him on a new spiritual path.