A half-century after his death, John III was canonized as a saint, under the name John the Merciful, and is commemorated annually on November 4. George Akropolites mentions that the people saw to the construction of a temple in his honour in Nymphaeum, and that his cult as a saint quickly spread to the people of western Asia Minor. On the same day, since 2010, the "Vatatzeia" festival is organized at Didymoteicho by the local metropolitan bishop. Alice Gardiner remarked on the persistence of John's cult among the Ionian Greeks as late as the early 20th century, and on the contrast she witnessed where "the clergy and people of Magnesia and the neighbourhood revere his memory every fourth of November. But those who ramble and play about his ruined palace seldom connect it even with his name."