Сигизмунд Кейстутович
Surviving documents attest that around 1437 a representative of the Raczków family, Jakub Tabutowicz of the coat of arms Łabędź, received from Michael Žygimantaitis son of Sigismund Kęstutaitis, Duke of Lithuania, a wilderness area along the river Biała that marked the beginning of Białystok as a settlement. Białystok administratively was part of the Podlaskie Voivodeship, after 1569 also part of the Lesser Poland Province of the Crown of the Kingdom of Poland.