Płock

Płock crowns a high bank of the Vistula, where Cathedral Hill carried the ducal stronghold of Mazovia and the bishops' cathedral. A bishopric had stood here since 1075, and from 1138 the town was the seat of the Mazovian Piast dukes. Prussian and Lithuanian raiders burned it more than once in the thirteenth century; it received town rights under Chełmno law in 1237, and about 1300 a new town was laid out beside the old one.

King Casimir III the Great held the duchy of Płock from 1351 to 1370. He joined the old and new towns, gave them Chełmno law and freedom from rents, and built a brick castle behind a double wall and moat, with the town walled in turn and entered by three gates. His successors Siemowit III and Siemowit IV minted their own coins and ruled as dukes of Mazovia. Siemowit's wife Alexandra, Jogaila's sister, founded the Holy Trinity hospital in 1405. When the last duke, Janusz II, died in 1495, John Albert joined the duchy to the Crown, and Płock became the capital of a voivodeship. After the Peace of Toruń of 1466 it grew rich on the trade from Toruń to Volhynia and on grain floated down the Vistula to Gdańsk; by 1564 it had about 600 houses, nearly as many as Warsaw. A fire in 1616 and the Swedish wars of 1656–57 then wrecked it, and in 1782 only 1,411 people lived there.