In 451 Atilla the Hun invaded the West. He was repelled by a coalition of forces lead by the General Aetius.
Also some great links from listener Jamie:
Here's a good account of the Battle of Chalons by military historians Dr. Aryeh Nusbacher and Dr. Saul David on a BBC show.
Start the video at 2 minutes, here is the full show if you like it:
There are other battles too, a handly list is here
And listener Tony:
Check out a replay of the Battle of Chalons here: