Copernicus spent most of his adult life in Warmia (Ermland), a dominium of the Bishop of Warmia and of the cathedral chapter, covering an area of 4250 km2 and occupying around one-third of the total area of the Diocese of Warmia (as marked out by the papal legate William of Modena in 1243).
In Copernicus’ time, it had a population of ca. 90,000 and an aerial view would show an irregular trapezoidal shape expanding south-eastwards from the Vistula Lagoon (Zalew Wiślany) to the towns of Reszel (Rössel) and Biskupiec (Bischofsburg), and the lake, Jezioro Łańskie. The borders of the diocese reached far beyond the dominium of the bishopric, embracing Elbląg (Elbing) in the west and reaching the River Pregoła to the north-east.
From 1466, surrounded by Teutonic Prussia (Prusy Krzyżackie) on three sides, the bishopric of Warmia had only limited direct access to the other territories of Royal Prussia (Prusy Królewskie) through a narrow strip alongside the Vistula Lagoon near the town of Tolmicko (Tolkemit). The nature of its location made it easier to safeguard the judicial, political, social, economic and administrative autonomy won when under the control of the Teutonic Order, and not only within the Kingdom of Poland but within the province of Royal Prussia as well. Until 1526 the Bishops of Warmia enforced church legislation within the entire diocese although formally they were answerable to the Metropolitan of Riga until this archbishopric was secularized in 1566.
Two-thirds of the dominium of Warmia, namely, the fiscal districts (Kammeraemter): Barczewo (Wartenburg), Braniewo (Braunsberg), Dobre Miasto (Guttstadt), Jeziorany (Seeburg), Lidzbark (Heilsberg), Orneta (Wormditt) and Reszel (Rössel), were under the jurisdiction of the bishop; whereas the remaining: Fromborskie (Frauenburg), Olsztyńskie (Allenstein) and Pieniężnieńskie (Mehlsack), were under the cathedral chapter of Frombork (Frauenburg). The bishop and the chapter had the same rights to exercise power over their respective territories; however, the bishop enjoyed legislative sovereignty over the chapter and was indeed the greatest landowner in Royal Prussia (Prusy Królewskie). He also represented his ‘mini-state’ at assemblies of the ‘Prussian estates’ while in 1508 he was actually elected chair of the Prussian Council (Rada Pruska). In the case of a vacancy or a prolonged absence, the chapter would assume full control over the dominium and so, until 1512, in practice it was the chapter decided whom to elect to the bishopric.
The strong position of the bishop and the chapter of Frombork (Frauenburg), although also resulting from their financial independence was, first and foremost, conditioned by the social and political structure of the dominium. Serfs made up the majority of the population (nearly 75%) and although there were some gentry, free peasants and burghers, they did not play an important role because, in reality, the bishop and the chapter subjugated nearly the entire population through the law and economic control. The deliberations of the sejmik in Lidzbark (Heilsberg) concerning taxation hardly made any difference and in practice only the bishop and delegates from the chapter represented their ‘mini-state’ outside its boundaries.