Huns.

This is coolbert:

One more from the book: "THE FALL of the ROMAN EMPIRE" by Arthur Ferrill.

1. With regard to the Roman general Aetius:

"Aetius saved the Western Roman Empire from the Huns, the scourge of God, and he stood out as a popular, active champion of Roman civilization at a time when the dynasty of Theodosius seemed lethargic, incompetent and degenerate. Possibly the great general did not deserve the high repute he achieved . . . but in the tragic drama of Rome's fall, history assigned him one of the leading, heroic roles."

2. And with regard to Chalons:

". . . the battle of Chalons was genuinely one of the great decisive battles in western history . . . it is true that the victory did not save the Roman Empire and that the Empire of the Huns might have collapsed on Attila's death anyway . . . Yet, as a a conflict between Christians and heathen, as an engagement that seemed to confirm Christian power in western Europe, indeed as a formidable, real blow to the power of the Huns in their relations with Rome, it was one of the world's most important battles."

See also the wiki entry as pertains to Chalons, the importance of the battle or the lack thereof, depending on perspective.

coolbert.