In the early 1900s, Białystok was reputed to have the largest concentration of Jews of all the cities in the world. In 1931, 40,000 Jews lived in the city, nearly half the city's inhabitants.The city is the seat of the Roman Catholic Archdiocese of Białystok. Establishment of the Diocese and the Archdiocese and the cities of Bialystok ended the period of the temporary church administration in the Bialystok region owned lands over the centuries to the Archdiocese of Vilnius, which after World War II remained in the Polish borders. The city is also the seat of the Bialystok-Gdansk Diocese of the Autocephalous Polish Orthodox Church. Bialystok is the largest concentration of Orthodox believers in Poland.