the commonwealth was formed at the union of lublin of 1569 from the kingdom of poland and the grand duchy of lithuania. the armies of those states differed from the organization common in the west of europe, as according to bardach, the mercenary formations (polish: "wojsko najemne"), common there, never gained popularity in poland. brzezinski, however, notes that foreign mercenaries did form a significant portion of the more elite infantry units, at least till the early 17th century. in the 15th century poland, several other formations formed the core of the military. there was a small standing army, "obrona potoczna" ("continuous defense") about 1,500–3,000 strong, paid for by the king, and primarily stationed at the troubled south and eastern borders. it was supplemented by two formations mobilized in case of war: the pospolite ruszenie (polish levée en masse – feudal levy of mostly noble knights-landholders), and the "wojsko zaciężne", recruited by the polish commanders for the conflict (it differed from western mercenary formations in that it was commanded by polish officers, and dissolved after the conflict has ended).