Ivan the great gave further substance to the idea that muscovy was the heir to rome after the fall of constantinople by

Constantinople was captured in 1453 by army of Ottoman Empire. That was end of Byzantine Empire. Ivan III of Russia wedded Sophia Paleologue, daughter of Thomas Palaeologus (brother of last Byzantine Emperor), so Ivan had mariage right to Byzanine throne. Ortodox canonist also suggested that Moscovy became new Rome.