Eannatum (Sumerian: 𒂍𒀭𒈾𒁺 É.AN.NA-tum₂; fl. c. 2450 BC) was a Sumerian Ensi (ruler or king) of Lagash. He established one of the first verifiable empires in history, subduing Elam and destroying the city of Susa, and extending his domain over the rest of Sumer and Akkad. One inscription found on a boulder states that Eannatum was his Sumerian name, while his "Tidnu" (Amorite) name was Lumma.

Eannatum, grandson of Ur-Nanshe and son of Akurgal, was a king of Lagash who conquered all of Sumer, including Ur, Nippur, Akshak (controlled by Zuzu), Larsa, and Uruk (controlled by Enshakushanna, who is on the King List).

He entered into conflict with Umma, waging a war over the fertile plain of Gu-Edin. He personally commanded an army to subjugate the city-state, and vanquished Ush, the ruler of Umma, finally making a boundary treaty with Enakalle, successor of Ush, as described in the Stele of the Vultures and in the Cone of Entemena:

32–38

𒂍𒀭𒈾𒁺 𒉺𒋼𒋛 𒉢𒁓𒆷𒆠 𒉺𒄑𒉋𒂵 𒂗𒋼𒈨𒈾 𒉺𒋼𒋛 𒉢𒁓𒆷𒆠𒅗𒆤
e₂-an-na-tum₂ ensi₂ lagaš^ki pa-bil₃-ga en-mete-na ensi₂ lagaš^ki-ka-ke₄
"Eannatum, ruler of Lagash, uncle of Entemena, ruler of Lagash"
39–42
𒂗𒀉𒆗𒇷 𒉺𒋼𒋛 𒄑𒆵𒆠𒁕 𒆠 𒂊𒁕𒋩
en-a₂-kal-le ensi₂ umma^ki-da ki e-da-sur
"fixed the border with Enakalle, ruler of Umma"
Extract from the Cone of Enmetena, Room 236 Reference AO 3004, Louvre Museum.

Eannatum made Umma a tributary, where every person had to pay a certain amount of grain into the treasury of the goddess Nina and the god Ingurisa.

Eannatum expanded his influence beyond the boundaries of Sumer. He conquered parts of Elam, including the city Az off the coast of the modern Persian Gulf, allegedly smote Shubur, and, having repulsed Akshak, he claimed the title of "King of Kish" (which regained its independence after his death) and demanded tribute as far as Mari:

"He (Eannatum) defeated Zuzu, the king of Akshak, from the Antasurra of Ningirsu up to Akshak and destroyed him."