 Although Ibbi-Sin baulked at promoting him, Ishbi-Erra had apparently succeeded in wrestling control over Isin by Ibbi-Sin's 8th year, when he began assigning his own regnal year-names, and thereafter an uneasy chill descended on their relationship.Ibbi-Sin bitterly lambasted Ishbi-Erra as “not of Sumerian seed” in his letter to Puzur-Šulgi and opined that