The city is the seat of the Roman Catholic Archdiocese of Białystok. Establishment of the Diocese and the Archdiocese and the cities of Białystok ended the period of the temporary church administration in the Białystok region owned lands over the centuries to the Roman Catholic Archdiocese of Vilnius, which after World War II remained in the Polish borders. The city is also the seat of the Białystok-Gdańsk Diocese of the Polish Orthodox Church. Białystok is the largest concentration of Orthodox believers in Poland.