During the initial stages of the Protestant Reformation, most Hungarians adopted first Lutheranism and then Calvinism in the form of the Hungarian Reformed Church. In the second half of the 16th century, the Jesuits led a Counterreformation campaign and the population once again became predominantly Catholic. This campaign was only partially successful, however, and the (mainly Reformed) Hungarian nobility were able to secure freedom of worship for Protestants. In practice, this meant ''cuius regio, eius religio''; thus, most individual localities in Hungary are still identifiable as historically Catholic, Lutheran, or Reformed. The country's eastern regions, especially around Debrecen (the "Calvinist Rome"), remain almost completely Reformed, a trait they share with historically contiguous ethnically Hungarian regions across the Romanian border.