In 51 CE, king Gotarzes II died. According to the Roman historian Tacitus, the Parthian ruler died of an illness,note[Tacitus, Annals 12.14.] although Josephus writes that he was assassinated.note[Josephus, Jewish Antiquities 20.74.] In any case, the new ruler was a man named Vonones II. Tacitus has only this to say:
Vonones, then viceroy of Media, was called to the throne. No successes and no reverses entitled him to mention: he completed a short, inglorious and perfunctory reign, and the Parthian empire devolved upon his son Vologases.note[Tacitus, Annals 12.14.]
Towards the end of 51, the reign of Vologases I had began.
The chronology of the Arsacid kings of the Parthian Empire is less well-understood than, for example, the sequence of Seleucid and Ptolemaic kings or the emperors of Rome. This information is based on the researches by G.R.F. Assar, as published in "Iran under the Arsakids, 247 BC – AD 224/227" in: Numismatic Art of Persia (2011).