Today, August 9, is the 1635th anniversary of the Battle of Adrianople, at which the Roman forces of the emperor Valens were routed by Fritigern’s army of Goths (together with some non-Goths) and at which Valens himself was killed. In 2013, so many years later, this may not seem to be a very momentous occasion, but in fact it was crucial for the history of the Roman Empire, and therefore for Europe and Christendom, for several hundred years to come. Valens was an Arian, and his death left a vacuum in the East.
To fill this vacuum, the emperor Gratian (whose colleague, Valentinian II, was only a boy) appointed the Spanish general Theodosius first as magister militum (master of soldiers) to war against the Goths, and then as Augustus on January 19, 379. Theodosius, unlike Valens, was a champion of Nicene orthodoxy; it was under his tutelage that the Nicene faith finally won out in the late fourth century and because of his policy that paganism was more rigorously suppressed.
The death of Valens, then, set in motion a series of events whose effects are still with us.