“The work started two years ago, and we couldn't even stand up straight,” archaeologist Tehillah Lieberman told NBC News. “We were crawling from a hole in the ceiling and dug it all by hand."
Lieberman's team was looking for a street that they suspected passed through the site from 530 B.C. to 70 A.D.
But the researchers were puzzled when they exposed the remnants. Eventually a circle-shaped structure started to emerge.
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“Everything got a lot more exciting since we understood we were exposing history,” Lieberman said.
Experts have been looking for a Roman theater since the dawn of archaeological research in Jerusalem more than 150 years ago.
The city was destroyed by the Romans in 70 A.D. and eventually turned into a Roman colony.
Based on historical writings, archaeologists knew that like any other city in the Roman Empire, Jerusalem had to have a theater.
What Lieberman and her colleagues unearthed looks a great deal like what generations of archaeologists before them were feverishly searching for.
Archaeologists had different opinions of where the theater might actually be, but it appears no one guessed that it would be hiding right next to the Western Wall itself.
Lieberman said the theater, which apparently seat about 200 people, is not like the bigger examples seen in other cities held by the Romans.
"It has the same structure, the same semicircular stepped building," she said. "It's just a lot smaller."
However, it is unclear whether the theater was ever actually used.
One of its staircases was never completely hewn. Some speculate that a Jewish revolt against Rome, which occurred from 132-135 A.D., might have halted construction and left the theater unfinished.
Lieberman says the find sheds more light on Jerusalem of the late Roman period, a time that historians don’t know much about.
Most of the major public structures from Roman Jerusalem — the large theater forum, basilica and bathhouse — have yet to be uncovered.
“Jerusalem was always inhabited and there were always different cultures and nations that lived here,” Lieberman said. “It's very hard to find the remains from the different periods. You usually find a foundation here, a wall there. But to find something standing completely whole doesn't happen so much in Jerusalem, especially not from the late Roman period."
Researchers have at least another 10 feet of ground below the theater to excavate to see what other discoveries may be awaiting underneath. The Israeli Antiquities Authority says the excavation site may eventually be opened to the public.
Paul Goldman reported from Jerusalem, and Yuliya Talmazan from London.
Paul Goldman is a Tel Aviv-based producer and video editor for NBC News.