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While you may not have heard of what happened at the location above on October 28 in the year 312 AD (1,696 years ago today), the Battle of the Milvian Bridge goes down in history as one of the most significant battles in world history.

First, the who/what/when/where...

The proximate cause was the system of power sharing set up by the previous emperor, Diocletian. He established a tetrarchy, basically dividing the empire up into four quadrants and establishing an emperor over each. Instead of dying in office, he decided to retire and -- I kid you not -- spend his days puttering about the gardens of his estate on the Adriatic Sea. He encouraged all the other mini-emperors to maintain an even keel and continue to share power.

This worked out about as well as you cynical WTH readers would imagine: they all started fighting for control of the whole enchilada. Especially since the system didn't allow for hereditary succession. When the emperor of the northwest quadrant died in 306 his son Constantine found himself and his troops faced with the prospect of being out of power. He and they were stationed in the British city of York at the time, and his legions responded by proclaiming him Augustus (primary emperor), which meant they had to leave England and make that a reality.

They moved to the continent and gained control of Gaul and the Northern Italian peninsula with victories at Turin and Verona. By October of 312 they found themselves approaching the city of Rome itself for a climatic battle with the forces of the only rival left standing, Maxentius.

The Milvian Bridge spans the Tiber River leading into the city itself. On the evening of October 27, Constantine was preparing to either besiege the city or fight his way across the bridge, depending on how Maxentius decided to defend it.

This is the part of the story where there is some dispute as to what exactly happened. Two contemporary historians (Lactantius and Eusubius), both more or less employed by Constantine, record that before the battle (one says the night before, one says some days before) he saw either the latin cross or a chi-rho symbol (a kind of stylized cross juxtaposing the first two letter in the greek word "christ" or "xristos" -- "chi" and "rho"). Anyway, when he saw this vision in the sky he heard the words, "In this sign, you shall conquer" in Greek and was commanded to place the symbol on the shields of his soldiers before the battle.

So Constantine did just that: he put the chi-rho/cross onto his soldiers shields and battle standards.

October 28 comes. Even though he had amply supplied the city and had withstood two previous sieges, Maxentius decides to bring his army out and contest the crossing of the bridge. At the end of the day Maxentius' army is crushed and Constantine enters the city, the new and unchallenged empire of a united Rome.

Because of the vision and victory of the chi-rho sign, Constantine goes on to mainstream the Christian religion. He uses the chi-rho sign on coins and official buildings and documents. He legalizes the religion, outlawing the previous persecution. He subsidizes bishops and churches. He goes on to sponsor and preside over a great doctrinal assembly, the Council of Nicea, with the state paying the cost of bringing bishops from all around the empire to a suburb of his new capitol city, Constantinople. Although Constantine himself avoids baptism until his deathbed (still being engaged in the routine rough politics of Roman emperors -- including assassinations of rivals), he arguably does more to advance and legitimize Christianity as the religion of the west than anyone before him since Peter and Paul.

No some will argue that the story about the vision before the battle was political propaganda: that Constantine decided to legitimize Christianity because it was politically advantageous to do so and the story was a fabricated justification for doing so. But why should we think that? Unless we believe that such a vision was impossible (which is more of a philosophical than a historical argument), why not take him at his word? While Constantine was no saint, after the Battle of Milvian Bridge he did become the greatest patron of the Christian religion to that point and set the course for Western Civilization to be Christian in religion, politics and culture. Nothing compelled him to do so, in fact some of his successors tried to undo his moves. And nothing compelled him to preside over the Council of Nicea and get a death-bed baptism, either. It seems to me that in the absence of some evidence to the contrary, we might as well take the man at his word: he felt that the Christian God had given him the victory and the empire, and felt motivated -- if not to become a humble and pious Christian -- to at least reward and patronize the worship of that God.

If you're interested and have time, here's a dramatic recreation of the battle: