In the 16th century the Commonwealth grew to almost 1 million km2, with a population of 11 million. It prospered from its enormous grain, wood, salt, and cloth exports to Western Europe via the Baltic Sea ports of Gdańsk, Elbląg, Riga, Memel, and Königsberg. The Commonwealth's major cities included Poznań, Kraków, Warsaw, Lviv, Vilnius, Toruń, and, for a time in the 17th century, Kiev. The Commonwealth army was able to defend the realm from foreign invasion, and also participated in aggressive campaigns against Poland's neighbors. As Polonization followed in conquered territories, at least among the politically influential classes, the Polish language became the "lingua franca" of Central and Eastern Europe.