The paper will focus on the analysis of the sworn formulas that were a crucial part of the annual city council renewal ceremony and on how this source can help us analyze the governance structures of late medieval and early modern municipalities and their changes. Attention will be paid to the cities of the Magdeburg Legal District, whose upper court of appeal was – until the establishment of the Court of Appeal in Prague – the Lower Silesian metropolis, city of Wroclaw. The oaths from the selected urban areas of northern Moravia and Silesia will be presented and analyzed in the long term perspective - from the beginning of the 15th to the end of the 18th century.