At the end of 1393 and early 1394, Bayezid I began gathering his Christian vassals at Serres. Byzantine sources tell that among the vassals were Stefan, Emperor Manuel II (1391–1425), his nephew John VII (1390) and his brother Theodore I of Morea (r. 1383–1407), and the Serbian lord Constantine Dragaš. It is believed that Bayezid I planned to kill the vassals at the meeting and take their lands. He gave the order to kill them, but it was not done immediately, then he changed his mind, after which some of them went home, while the rest of them completed the conquest of Thessaly and Thessaloniki (12 April).