John Sigismund's most significant action was his conversion from Lutheranism to Calvinism, after he had earlier equalized the rights of Catholics and Protestants in the Duchy of Prussia under pressure from the King of Poland. He was probably won over to Calvinism during a visit to Heidelberg in 1606, but it was not until 25 December 1613 that he publicly took communion according to the Calvinist rite. The vast majority of his subjects in Brandenburg, including his wife Anna of Prussia, remained deeply Lutheran, however. After the Elector and his Calvinist court officials drew up plans for mass conversion of the population to the new faith in February 1614, as provided for by the rule of Cuius regio, eius religio within the Holy Roman Empire, there were serious protests, with his wife backing the Lutherans. Resistance was so strong that in 1615, John Sigismund backed down and relinquished all attempts at forcible conversion. Instead, he allowed his subjects to be either Lutheran or Calvinist according to the dictates of their own consciences. Henceforward, Brandenburg-Prussia would be a bi-confessional state.[1]
Family and children
On 30 October 1594, John Sigismund married Anna of Prussia, daughter of Albert Frederick, Duke of Prussia (1553–1618). She was the elder sister of his stepmother. They were parents to eight children: