Sochaczew in the context of "Siemowit IV, Duke of Masovia"

Siemowit V of Rawa was a Polish prince of the House of Piast from the Masovian branch. He ruled as Duke of Rawa Mazowiecka, Płock, Sochaczew, Gostynin, Płońsk, Wizna, and Belz from 1426 to 1434 with his brothers, and after the 1434 division of their inheritance, solely over Rawa Mazowiecka, Gostynin, and Sochaczew.

Czersk Land (Polish: ziemia czerska, named after the town of Czersk) was an administrative unit (ziemia) of the Kingdom of Poland and the Polish–Lithuanian Commonwealth. With its capital in the town of Czersk, it belonged to the Masovian Voivodeship.

The history of Czersk Land as a separate administrative unit dates back to 1245, when Duke Konrad I of Masovia moved the seat of the castellany from Grójec to Czersk, making Czersk the major urban and political center of southern Mazovia. In 1377, Siemowit III, Duke of Masovia called a council in Sochaczew, during which he disbanded castellanies, and following the example of the Kingdom of Poland, created ten lands, all divided into counties. Therefore, the Land of Czersk was established, with three counties: Czersk, Warka and Grójec. It stretched from Mińsk Mazowiecki to Grojec, along both banks of the Vistula, including the town of Garwolin.