No ornaments or weapons were found with the bodies, the archaeologist added.
"It does look as if, after everyone died, that somebody has gone through the battlefield and extracted things of value," she said.
Large quantities of broken pottery vessels along with bones from goats, sheep, and up to 200 cattle lie over the dead. This suggests the burials were marked by a huge feast, according to findings to be published later this year in the archaeology journal Iraq.
Such an event may represent a celebration of the victors over the vanquished or mark an act of remembrance, McMahon said.
"There's definitely a feast, but whether it's a great victory celebration or it's the commemoration of a battle in which a lot of locals died, that's something we're not yet quite sure of," she added.
The study team hopes carbon and nitrogen isotope analysis of the victims' teeth will provide an answer.
The analysis should reveal important clues about the victims' diet, showing whether those buried lived locally or not, McMahon said.
"Worth Fighting For"
Other recent finds at Tell Brak may explain why the city was worth fighting over, McMahon said.
Excavations led by Joan Oates of the McDonald Institute for Archaeological Research at the University of Cambridge show the settlement was a thriving center of trade and industry in the centuries leading up to the massacre.
Discoveries include large quantities of imported raw materials such as obsidian, flint, jasper, marble, bitumen, and shells that were used for their decorative mother-of-pearl inlay.
Manufactured items have also been found, including a skillfully crafted obsidian drinking vessel glued to a marble base using bitumen, a viscous oil extract.
A study published recently in the journal Science revealed that Tell Brak began growing rapidly in size around 6,200 years ago, becoming one of the world's earliest urbanized settlements.
The study showed that Tell Brak grew from the outside in, as separated settlements grew more dense and formed a city center.
Lead researcher Jason Ur, from Harvard University in Massachusetts, said the urbanization of Tell Brak "tells us about the formation of the very first cities in the world."
Ur pointed out that excavations show the city was home to a substantial concentration of wealth and political power.
The city would have had "the ability to field armies, engage in monumental construction efforts, and create the agricultural surpluses necessary to sustain a nonproducing social elite," he said. "Therefore Brak would certainly have been worth fighting over.
"Given Brak's status as one of the earliest cities in the Near East," he added, "it is not impossible that this violence was the result of growing pains—internal social conflict brought about by the processes of urbanization, an entirely new phenomenon at this early date."
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