20 Zlotys Union of Lublin

The Union of Lublin, signed in 1569, merged the Kingdom of Poland and the Grand Duchy of Lithuania into the Polish-Lithuanian Commonwealth — at the time, the largest state in Europe by land area. The union was driven largely by Lithuanian nobility seeking the same legal privileges enjoyed by Polish szlachta, and by Sigismund II Augustus, who died childless four years later and saw the merger as his dynastic endgame.

The rectangular format of this issue is not decorative novelty — NBP has used non-circular formats selectively since the 1990s to distinguish collector commemoratives from circulation coinage.