Complex sentence: Tacitus, "Annals", According to Tacitus and Cassius Dio, the Younger Drusus and Sejanus began bickering and entered a feud during which Drusus became ill and died of seemingly natural causes on 14 September AD 23.
Split into simpler sentences: Tacitus, "Annals", According to Tacitus and Cassius Dio, the Younger Drusus and Sejanus began bickering and entered a feud. During this time, Drusus became ill and died of seemingly natural causes on 14 September AD 23.