A team led by Professor Stuart Campbell and Dr. Jane Moon of the University of Manchester first spotted the football field-sized structure on a satellite on the site of Tell Khaiber in southern Iraq.
The team carried out a geographical survey and trial excavations of the site to confirm its size -- 80 meters on each side -- and approximate age -- about 4,000 years old.
The structure is believed to be an administrative center of Ur, with an arrangement of rooms situated around a large courtyard.
"We provisionally date the site to around 2,000 BC, the time of the sack of the city and the fall of the last Sumerian royal dynasty," Campbell said. "The surrounding countryside, now arid and desolate, was the birthplace of cities and of civilization about 5,000 years ago and home to the Sumerians and the later Babylonians."
Campbell, Moon and their team of six British and four Iraqi researchers are the first to excavate Southern Iraq since the 1980s, when Saddam Hussein was in power.
"It has been off-limits to international archaeologists for many decades so the opportunity of re-engaging with the study of the earliest cities is a truly exciting one," Campbell said.