In 1510 Michał Pac became the governor of the area, founding the settlement of Beržininkai (). This started a period of the rapid development of the former Yotvingian lands. On December 22, 1522, Sigismund I the Old ordered the voivode of Podlaskie Janusz Kostewicz to grant half of a square mile of land at the shores of the river Sejna (now called Marycha) to hetman Iwan Wiśniowiecki. On May 21 of the following year, Kostewicz described the parcel in a letter to the king and soon afterwards Wiśniowiecki became the owner of the area. A new wooden manor was built in the place where the Sejna river reached Sejny lake and soon settlement started. Wiśniowiecki, a mighty magnate from Volhynia, never came there personally and instead appointed his governor to rule the hamlet.