The purpose of the article is to state the reasons for changing sessions’ places and dates
of the General Sejmiki, with particular emphasis on the years 1480-1542. Despite established regulations (including the constitution of April 12, 1521 and the so-called Prussian Constitution of July 17, 1526), this happened repeatedly. What was the reason? First, it will be presented the history of the creation of Royal Prussia and the development of the state assembly system in this Polish province.