Piotrków became part of the Polish–Lithuanian Commonwealth in 1569. When the seat of the Parliament was moved to Warsaw, the town became the seat of the highest court of Poland, the Crown Tribunal, and trials were held there from 1578–1793; the highest Lithuanian court was held in Grodno. Piotrków's Jewish population was expelled in 1578 and only allowed back a century later. The town became a post station in 1684. Around 1705, German settlers (often Swabians) arrived in the town's vicinity and founded villages; they largely retained their customs and language until 1945.