In June 1422, John VIII Palaiologos supervised the defense of Constantinople during a siege by Murad II, but had to accept the loss of Thessalonica, which his brother Andronikos had given to Venice in 1423. To secure protection against the Ottomans, he made two journeys to Italy in 1423 and 1439. In 1423 he became the last Byzantine emperor (the first since emperor Constans II´visit in 663) to make a visit to Rome. During the second journey he visited Pope Eugene IV in Ferrara and consented to the union of the Greek and Roman churches. The Union was ratified at the Council of Florence in 1439, which John attended with 700 followers including Patriarch Joseph II of Constantinople and George Gemistos Plethon, a Neoplatonist philosopher influential among the academics of Italy. The Union failed due to opposition in Constantinople, but through his prudent conduct towards the Ottoman Empire he succeeded in holding possession of the city.