As such, the Babylonians might have interpreted them as failing in their duties as kings and thus not having the necessary divine endorsement to be considered true kings of Babylon.[7] In response to this, Babylon revolted several time against Persian rule in an attempt to regain its independence, though known revolts (with the possible exception of Nidin-Bel's revolt) are restricted to the early Persian period. The Persian king Darius I (r. 522–486 BC) faced the rebellions of Nebuchadnezzar III (522 BC) and Nebuchadnezzar IV (521 BC), both of whom claimed to be sons of Nabonidus, Babylon's last independent king.[8][9] Darius I's son and successor, Xerxes I (r. 486–465 BC), also faced two Babylonian revolts, two contemporary uprisings in 484 BC led by the rebels Bel-shimanni and Shamash-eriba.[10] The revolts against Xerxes in particular led the Persians to incur retribution on the Babylonians.