By 526–527, overt fighting between the two empires had broken out in the Transcaucasus region and upper Mesopotamia; the Persians continued to exert pressure on the Romans to obtain funds from them. Following the emperor Justin I's death in 527, Justinian I acceded to the imperial throne. The early years of war favored the Persians, by 527 the Iberian revolt had been crushed, a Roman offensive against Nisibis and Thebetha in that year failed and forces attempting to fortify Thannuris and Melabasa were prevented from doing so by Persian attacks.