Duchy of Silesia

State · 1139–1304 CE · at its largest around 1139 CE

Duchy in south-western Poland assigned to Wladyslaw II the Exile under Boleslaw III's testament, which his descendants later split into many smaller Silesian duchies.

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).