Located in a valley on the northern bank of the lower Zab River, the remains of the city, called Idu, are now part of a mound created by human occupation called a tell, which rises about 32 feet above the surrounding plain.
The earliest remains date back to Neolithic times, when farming first appeared in the Middle East, and a modern-day village called Satu Qala now lies on top of the tell.
The city thrived between 3,300 and 2,900 years ago, said Cinzia Pappi, an archaeologist at the Universitat Leipzig in Germany.
As the empire declined, the city gained its independence and became the centre of a kingdom that lasted for about 140 years, until the Assyrians reconquered it, 'LiveScience' reported.
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The researchers were able to determine the site's ancient name when, during a survey of the area in 2008, a villager brought them an inscription with the city's ancient name engraved on it. Excavations were conducted in 2010 and 2011.
Two works of art unearthed by researchers hint at the decorations adorning the palaces at the time Idu was independent.
Above and below the sphinx, a surviving inscription reads, "Palace of Ba'auri, king of the land of Idu, son of Edima, also king of the land of Idu."
Another work that was created for the same ruler, and bearing the same inscription as that on the sphinx, shows a "striding horse crowned with a semicircular headstall and led by a halter by a bearded man wearing a fringed short robe," authors wrote in the journal Anatolica.
The scene would have shown a bow-wielding man crouching down before a griffon, as well as a morning star (a symbol of the goddess Ishtar), a lunar crescent (a symbol of the moon god) and a solar disc symbolising the sun god.