Ekallatum, whose name means "the palace," became the capital of an Amorite dynasty related to Assyria, which was important in the 19th and 18th centuries BCE period. The history of upper Mesopotamia in this period is documented in the archives of Mari, Syria.
Its first known king was Ila-kabkabu, who seems to have entered into a conflict with Iagitlim of Mari. His son Shamshi-Adad I ascended to the throne around 1810 BCE, continuing the conflict and attempting to extend into the valley along the Khabur River. His expansion was halted by Iagitlim's son, Iakhdunlim, and he was soon after defeated by Naram-Sin of Assyria, which caused him to flee to Babylon, a city founded and ruled by fellow Amorites. He returned upon Naram-Sin's death. Soon thereafter, a series of military victories by Shamshi-Adad followed, and he seized all of Upper Mesopotamia, usurping Erishum II as king of Assyria. He founded his own capital at Shubat-Enlil, entrusting Ekallatum to his elder son Ishme-Dagan. (His other son, Yasmah-Adad, was placed on the throne of Mari at the time.) Ishme-Dagan appears to have been a capable military leader, but when his father died in around 1775, he proved unable to maintain the whole kingdom; nonetheless, he kept Ekallatum, while his brother lost Mari and was killed.
The reign of Ishme-Dagan was chaotic. Unable to restore power to the city despite his many attempts, he was the target of nearby warlords, in particular, Zimrilim of Mari. When the Elamites took Ekatallum in 1765, he sought refuge with his traditional ally -- Hammurabi of Babylon -- who helped him take back the throne. Consequently, Ekallatum became a vassal city subservient to the king of Babylon, who came to control all of Mesopotamia. With the death of Ishme-Dagan, his son Mut-Ashkur succeeded him. He was the last known king of Ekallatum, and the city disappeared thereafter from Mesopotamian history. Mut-Ashkur is listed as king of Assyria, and it would appear that Ekallatum was absorbed by Assyria.