 This caused Sextus to lose many valuable allies as the formerly exiled senators gradually aligned themselves with either Octavian or Antony.To secure the peace, Octavian betrothed his three-year-old nephew and Antony's stepson Marcus Claudius Marcellus to Sextus' daughter Pompeia.With peace in the West secured, Antony planned to retaliate against Parthia by invading their territory.