While such were his relations with the Byzantine Empire and the rival Republics of the West, the Papacy regarded Francesco as one of the factors in the Union of the Churches and thereby as a champion of Christendom against the Turks. When Innocent VI in 1356, despatched St Peter Thomas and another bishop to compass the Union of the Old and the New Rome, he recommended his two envoys to the lord of Lesbos. Thirteen years later, Francesco accompanied his brother-in-law, the Emperor John V, to Rome, and signed as one of the witnesses of that formal confession of the Catholic faith, which the sorely-pressed sovereign made on October 18, 1369, in the palace of the Holy Ghost before Urban V[534]. He was one of the potentates summoned by Gregory XI in 1372 to attend the Congress[535] of Thebes on October 1, 1373, to consider the Turkish peril—a peril which at that time specially menaced his island—and in the following year the Pope recommended Smyrna to his care, and sent two theologians to convince him, a strenuous fighter against the Turks, and defender of Christendom beyond the seas, that the Union of the Churches would be a better defence against them than armed force[536]. The Popes might well have thought that no one could be a better instrument of their favourite plan than this Catholic brother-in-law of the Greek Emperor. But the astute Genoese was too wise to compel his Greek subjects to accept his creed. Throughout his reign, besides a Roman Catholic Archbishop, there was a Greek Metropolitan of Mytilene, and under his successor the Metropolitan throne of Methymna was also occupied[537]. The Armenian colony, settled in Lesbos, preferred, however, to seek shelter in Kos under the Knights of St John rather than remain as his subjects, without proper protection from a hostile raid[538].