Biecz flourished under Jagiellonian rule. The crown's encouragement of growth and trade, as well as the town's favorable location, were major influences on Biecz's rapid growth during this period. Under the rule of King Casimir IV Jagiellon, the town built its first municipal water supply. Inhabitants were also granted a number of privileges, such as relief from duties on various imported commodities. Additionally, merchants entering Polish territory were required to pass through Biecz, wherein taxes and other import tariffs were levied. This practice was established by Louis I of Hungary in 1372 along the Hungarian-Red Ruthenian trade route.