 The Muscovy population was Eastern Orthodox and preferred to use the Greek transliteration "Rossia" (Ῥωσία) rather than the Latin "Ruthenia".In the 14th century the southern territories of ancient Rus', including the principalities of Galicia–Volhynia and Kiev, became part of the Grand Duchy of Lithuania, which in 1384 united with Catholic Poland in a union which became the Polish–Lithuanian Commonwealth in 1569.Due to their usage of the Latin script rather than the Cyrillic script, they were usually denoted by the Latin name "Ruthenia".