In the winter of 1242-43, the Mongols under Bayju attacked Erzurum; the city fell without a siege. The Mongols prepared to invade Rum in the spring. To meet the threat, Kaykhusrev assembled soldiers from his allies and vassals. Simon of Saint-Quentin, an envoy of Pope Innocent IV on his way to the Great Khan, offers an account of the sultan’s preparations. He reports that the king of Armenia was required to produce 1400 lances and the Greek Emperor of Nicaea 400 lances. Both rulers met the sultan in Kayseri to negotiate details. The Grand Komnenos of Trebizond contributed 200, while the young Ayyubid prince of Aleppo supplied 1000 horsemen. In addition to these, Kaykhusrev commanded the Seljuq army and irregular Turkmen cavalry, though both had been weakened by the Baba Ishak rebellion.