The Eastern Orthodox Churches trace their roots back to the Apostles and Jesus Christ. Apostolic succession established by the seats of Patriarchy (for example see the Greek Orthodox Patriarch of Jerusalem). Eastern Orthodoxy reached its golden age during the high point of the Byzantine Empire, taken over by the Bulgarian Orthodox Church and the Serbian Orthodox Church before it continued to flourish in Russia after the Fall of Constantinople. Numerous autocephalous churches have been established in Eastern Europe and Slavic areas.