For thousands of years, the brutal battle had been lost to history. Around 3500 B.C., just across the Iraqi border in present-day Syria, an invading army from the south laid waste to a strategic city.

The invaders showered the city with hundreds of small clay missiles, knocked down fortification walls, burned buildings and perhaps took inhabitants captive.

This clearly was no minor skirmish," said Clemens Reichel of the University of Chicago's Oriental Institute. "This was 'shock and awe' in the fourth millennium B.C."

Reichel and Salam Al Kuntar, of Syria's Antiquities Department and Cambridge University, directed a team that excavated the site in the present day town of Hamoukar. It's one of the most revealing discoveries yet of early urban warfare.

There's no record of a battle, since writing hadn't been invented yet. In such cases, it's often difficult to determine whether destruction was the result of warfare or of other calamities such as accidental fires.

"But in our case, it was unambiguous," Reichel said. "There's very clear evidence of violent destruction."