After the death of King Zygmunt I. The General Sejm in Piotrków. 1548 r.
The decision to convene the Sejm was announced in June 1548 two months after the death of the long-reigning King Zygmunt I. The pre-Sejm regional assemblies were held in July 1548. The Sejm session opened on October 31, 1548. The Marshal was Jan Sierakowski, the Inowrocław military tribune. The Sejm dealt with issues of Turkish threat, coins, and correction of some rights. A heated debate revolved around the marriage of King Zygmunt August with Barbara Radziwiłłówna. The king's marriage without the senators' advice was considered a breach of common law and the magnates’ legitimate rights. The Sejm concluded its deliberations on December 12, 1548.
See: Diariusze sejmów (The Sejm Records 1548, 1553 and 1570). Publishers J. Szujski, Kraków 1872; L. Kolankowski, Zygmunt August, Grand Duke of Lithuania until 1548, Lwów 1913; Z. Wojciechowski, Zygmunt Stary, Warsaw 1946; S. Cynarski, Zygmunt August, Wrocław 1988; A. Sucheni-Grabowska, Zygmunt August, Polish King and Grand Duke of Lithuania 1520-1562, Warsaw 1996; A. Sucheni-Grabowska, Sejm in the years 1540-1587, in: History of the Polish Sejm, vol. 1, Warsaw 1984, edited by J. Michalski, pp. 114-216. Ustawodawstwo (Legislation), see Volumina Constitutionum, Vol. 1, part II, prepared for print by W. Uruszczak, S. Grodziski, I. Dwornicka, Warszawa 2000, pp. 78-83.