The country of Upi is mentioned in Mesopotamian tablets, between 4500 and 2000 BCE. A tablet of royal dynasties lists shows a so-called dynasty of Upi in Akkadian, Opis in Greek, with 6 kings who have ruled for 99 years, before a dynasty of Kish.
The 6 sovereigns are Unzi (30 years), Undalulu (12) Ursag (6), Sir Basha (20) Ishuil (24) and Shu Enzu (7). At that time, the city of seems to be the capital of Upi.
But most historians, relying on other later texts, consider that Opis was located to the east of the Tigris, at the confluence of Diyala. They make this positioning relative to the hypothetical location of Kish at Tell el-Oheimir and later texts from tablets of the dynasty of Ur-Nanshe.
Here are several excerpts which are difficult to position in time:
Eannatum defeated Zuzu, king of Akshak. This enabled him to obtain the kingship of Kish;
Kish undertook a war against Eannatum but Eannatum sent the king of Akshak in his country.
Eannatum has confronted Kish, Mari and Akshak.
I think that Akshak is the tell Es-Sakan, a town of Upi, located therefore between Egypt and Mesopotamia. And the facts reported by the tablets are conflicts between southern Levant and the Mesopotamia, with the control of Egypt (Kish called at that time) to the key. It is possible that this region of the Arabian Peninsula was less desert than today and the vast region of the west to Babylon to Damascus was this political entity.
Tablets, found both in Babylonia and Ebla, reinforce this hypothesis. They evoke the conquer of Akshak and a victory over Kish by Enshakushanna, who claims to have sacked Kish and captured Enbi-Eshtar, the King of Kish.
I think that these are disputes related to Sargon of Akkad who is deemed to have started his career with a king of Kish. Enshakushanna may be his Mesopotamian name.
In different hieroglyphic texts of Egypt, and in those of Tanis, a temple of Amon of Ope (Upi) is mentioned. A statue of Hori in the Berlin Museum, of which only the upper part following the bombings, has been studied by Yoyotte, it had a destination mention: the Osirian sanctuary Opé.
These are the reasons that make me position this country of Upi / Opis in the Levant in the 3rd millennium BC, as in the 2nd millennium BC (see here).
However, a so-called Opis city should exist in Mesopotamia during the Iron Age, because this is the name of a battle of the Persian king Cyrus II and the town is mentioned extensively in the history of Alexander the Great.
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My notes of veracity :
During the 3rd millennium BC, the country of Upi was located in the Levant : 3/5