Duchy of Masovia

State · 1139–1351 CE · at its largest around 1147 CE

Duchy in east-central Poland around Plock and later Warsaw, ruled by a branch of the Piasts; Konrad of Masovia invited the Teutonic Knights to the region.

On its lands while it lasted

Plock (c. 1139 CE): Capital of Duchy of Masovia (1139–1351).
Sandomierz (c. 1139 CE): Capital of Duchy of Sandomierz (1139–1304).
Poznań (c. 1139 CE): Capital of Duchy of Greater Poland (1139–1304).
Opole (c. 1177 CE): Capital of Duchy of Opole (1177–1304).
Bytom (1200 CE): Capital of Duchy of Bytom (1285–1304).
Kalisz (c. 1210 CE): Capital of Duchy of Kalisz (1210–1219).
Codex Gigas (c. 1229 CE): The largest surviving medieval European manuscript, written at the Benedictine monastery of Podlazice in Bohemia and nicknamed the Devil’s Bible for its full-page picture of the devil. Taken by Swedish troops in 1648, it is in Stockholm.
Battle of Legnica (1241 CE): Mongol forces defeated a Polish and Moravian army under Duke Henry II the Pious in Silesia.
Glogow (c. 1250 CE): Capital of Duchy of Glogow (1250–1313).
Kaliningrad (1255 CE): Capital of Duchy of Prussia (1526–1618).
Königsberg (1255–1945 CE): Capital of Duchy of Prussia (1526–1618), Brandenburg-Prussia (1619–1701).
Legnica (1264 CE): Capital of Duchy of Legnica (1279–1313).
Malbork Castle (1274 CE): Brick castle begun by the Teutonic Knights in 1274, later the order's headquarters; the largest castle in the world by land area.
Jawor (c. 1279 CE): Capital of Duchy of Jawor (1279–1313).
Racibórz (c. 1285 CE): Capital of Duchy of Racibórz (1285–1304).