As the waters of the Mosul dam reservoir in northern Iraq receded last fall, they revealed a stunning sight: a Bronze Age palace, many of its mud-brick walls and carefully planned rooms remarkably preserved.

The site, known as Kemune, has been known to researchers since 2010, when the reservoir had previously shrunk. The area had first flooded in the 1980s, when the Mosul Dam was constructed. But not until a drought hit the region last year did the water retreat enough for archaeologists to excavate.

When they did, they found not only the palace’s walls and rooms, but the remains of bright blue and red murals and cuneiform clay tablets, which are being translated. The expedition could shed light on a little-known empire that dominated the region from approximately 1500 to 1350 B.C.

The University of Tübingen in Germany and the Kurdistan Archaeology Organization announced the discovery Thursday, and a lead archaeologist, Hasan Ahmed Qasim, called it “one of the most important archaeological discoveries in the region in recent decades."

Qasim, a member of the Duhok Directorate of Antiquities, led the project along with Ivana Puljiz of the University of Tübingen. For about three and a half weeks in September and October, they worked feverishly to excavate the site before the waters returned.

“The main reason why we started excavating there was the discovery of colorful wall paintings on the surface of the site,” Puljiz told The Washington Post via email. “However, at that time we did not know to what kind of building these paintings belonged. This became clear only after we had excavated the architectural remains and realized how extensive they are.”

The researchers say they believe the site, in the Duhok province of Iraq’s Kurdistan region, dates from the Mittani Empire, a kingdom that spread across northern Mesopotamia and Syria. Little is known about its reign, but previous archaeological discoveries suggest that its kings probably interacted with Egyptian pharaohs and the Babylonians. By the 13th century B.C., the Mittani Empire was on the decline, and it was eventually absorbed by its better-known successors, the Hittites and Assyrians.

Each day of the dig, the water level receded, Puljiz said, eventually revealing a monumental terrace wall in the west of the palace that had been completely submerged at the start of excavation. By the end of their fieldwork, the remains of the palace were some seven meters (approximately 23 feet) high.

Further digging revealed numerous rooms, eight of which were excavated. When it was inhabited, the palace would have overlooked the Tigris River, giving residents an impressive view. Archaeologists found large fired bricks, which were used as floor slab. But Puljiz’s favorite discoveries were the paintings and 10 cuneiform tablets that could reveal even more of Kemune’s secrets.

“Wall paintings of this period are rarely found in archaeological excavations,” she said. In the team’s news release, she called them “an archaeological sensation.”

“The cuneiform texts we found in four rooms of the palace are no less important and will hopefully contribute to better understand the political and administrative organization of the Mittani Empire,” she added.

According to the researchers’ release, one of the tablets suggests that the site may be an ancient city known as Zakhiku, and the archaeologists say the palace may have existed for as many as 400 years.

Much mystery remains about the palace, but for now, Qasim, Puljiz and their colleagues will have to glean clues from what they collected last fall. Heavy rain returned to the area in the winter, and Kemune was submerged once more.

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