To secure protection against the Ottoman Turks he visited the pope and consented to the union of the Greek and Roman churches, which was ratified at Florence in 1439. He was accompanied by George Gemistos Plethon, a Neoplatonist philosopher who very influential among the academics of Italy and influenced the western European Renaissance, which was just beginning. The proposed church union failed, but by his prudent conduct towards the Ottoman Empire he succeeded in holding possession of Constantinople, and in 1432 withstood a siege by Sultan Murad I.
He was succeeded by his brother Constantine XI.
This entry was originally from the 1911 Encyclopedia Britannica.