Around 1490, the combined population of Poland and Lithuania, in a personal union (the Polish–Lithuanian union) since the Union of Krewo a century before, is estimated at about 8 million.[4] An estimate for 1493 gives the combined population of Poland and Lithuania at 7.5 million (including 3.9 million in the Kingdom of Poland[5]), breaking them down by ethnicity at 3.25 million Poles, 3.75 million Ruthenians and 0.5 million Lithuanians.[6] The Ruthenians composed most of the population of the Grand Duchy of Lithuania: this is the reason that the late GDL is often called a Slavic country, alongside Poland, Russia etc. In time, the adjective "Lithuanian" came to denote a Slav of the Grand Duchy.[7]