There are so many possible answers to this question. Pick one battle that intrigues you the most. It doesn't have to be from OIF/OEF.
for those of you who don't know, the oldest recorded war in history occurred in c. 2700 B.C. It was between Sumer (in modern Iraq) and Elam (a region that is now part of Iran), and was fought in the area around Basra (just like the Iran-Iraq war of the 1980s). Of course, tribes, cities, etc., had been fighting each other for thousands of years before that, but there are no records of these earlier conflicts as writing wasn't invented until a little before 3000 B.C.
And now you know!