Yousef or Dhu Nuwas (the one with sidelocks ) as known in Arabic literature, believed that Christians in Yemen were a fifth column .  Christian sources portray Dhu Nuwas (Yousef Asar) as a Jewish zealot, while Islamic traditions say that he threw 20,000 Christians into pits filled with flaming oil.  This history, however, is shrouded in legend.  Dhu Nuwas left two inscriptions, neither of them making any reference to fiery pits. Byzantium had to act or lose all credibility as protector of eastern Christianity. It is reported that Byzantium Emperor Justin I sent a letter to the Aksumite King Kaleb , pressuring him to "...attack the abominable Hebrew."  A tripartite military alliance of Byzantine, Aksumite, and Arab Christians successfully defeated Yousef around 525–527 AD, and a client Christian king was installed on the Himyarite throne.