During the first half of the 16th century, Biecz was one of the largest Polish cities both in size and population. The wars with Sweden as well as numerous fires caused the population to begin to decrease. In 1721, a great plague struck Biecz. The thirty survivors built a memorial chapel to St. Michael the Archangel in memory of the victims. Nazi occupation during World War II resulted in significant population losses. A number of smaller villages were resettled into Biecz during this time, resulting, in 1944, in a population of 5,973, the highest recorded population in history.