The name Belarus is closely related with the term Biełaja Ruś, i.e., White Rus'. There are several claims to the origin of the name White Rus'. An ethno-religious theory suggests that the name used to describe the part of old Ruthenian lands within the Grand Duchy of Lithuania that had been populated mostly by Slavs who had been Christianized early, as opposed to Black Ruthenia, which was predominantly inhabited by pagan Balts.