For the inaugural article in our new series “Big Questions,” The Gospel Coalition asked four Christian historians, “After AD 70, what day most changed the course of Christian history?” Robert Louis Wilken … at the University of Virginia. … George Marsden … at the University of Notre Dame… Philip Jenkins … at Baylor University. … Thomas S. Kidd … at Baylor University.

For the inaugural article in our new series “Big Questions,” The Gospel Coalition asked four Christian historians, “After AD 70, what day most changed the course of Christian history?”

Robert Louis Wilken is William R. Kenan professor emeritus of the history of Christianity at the University of Virginia. His most recent book is The First Thousand Years: A Global History of Christianity.

A good case can be made for the Muslim invasion of the Middle East in mid-seventh century, let us say AD 650. No event during the first millennium was more unexpected, more calamitous, and more consequential for Christianity than the rise of Islam. Few irruptions in history have transformed societies so completely and irrevocably as did the conquest and expansion of the Arabs in the seventh century. And none came with greater swiftness. Within a decade three major cities in the Byzantine Christian Empire—Damascus in 635, Jerusalem in 638, and Alexandria in 641—fell to the invaders. Most of the territories that were Christian in the year 700 are now Muslim. Nothing similar has happened to Islam. Christianity seems like a rain shower that soaks the earth and then moves on, whereas Islam appears more like a great lake that constantly overflows its banks to inundate new territory.

George Marsden is professor emeritus in history at the University of Notre Dame and the author of Jonathan Edwards: A Life.

I think it has to be the day that Constantine was converted to Christianity. That had huge effects both for good and for ill ever after.

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