The city of Harran appears in some of Mari tablets, including V75 which evokes the presence of troops controlling the neighbouring. This text certifies that the town existed at least since the beginning of the 2nd millennium BC.
It is also mentioned in the archives of Hattusa. Here is an extract of KUB XXIII 102 which lists the main cities in the area: "I conquered and destroyed them from the city of Irridu. The great gods have given me to govern all the countries of Taidu to Irridu and Eluhut with all Kasiyari Mountains, the fortresses of Sudu and Harranu to the bank of the Euphrates. "
Three stelae engraved with cuneiform characters have been found in reuse in the ruins of the Great Mosque of Harran in 1956. They refer to a Babylonian king named Nabonidus, who ruled from 556 to 539 BC. The presence of these stelae is explained by the local origin of his mother.
The Greeks knew the town under the name of Carrhae. Moreover, in the Bible, Harran is the city of the father of Abraham.
My notes of veracity :
Harranu was the present city of Harran: 4/5