From 1516 to 1521, Nicolaus Copernicus lived at the town's castle as administrator and in Mehlsack (Melzak, now Pieniężno). Copernicus was in charge of the Polish defenses in the Siege of Allenstein during the Polish-Teutonic War of 1519–21. He also started and managed the repopulation of the region, inviting a new wave of Polish settlers from Mazovia. The town along with Warmia then entered what is considered the region's golden age, crafts and trade developed, also due to the city's location on the Warsaw-Königsberg (Królewiec) trade route. During this period, the city was still visited several times by Copernicus, as well as leading figures of Polish Renaissance, writers, royal secretaries and diplomats: Johannes Dantiscus, called the "father of Polish diplomacy", and Marcin Kromer, who was also a historian and music theorist. The St. James' Pro-Cathedral, one of the most distinctive landmarks of the cityscape, was completed.