Greek Christianity was one of the original denominations of Christianity, originating with the apostolic churches founded in the Balkans and the Middle East during the 1st century AD. The church was centered around the Eastern Roman capital of Constantinople (now Istanbul, Turkey), and it differed from Latin Christianity in that Greek was its liturgical and traditional language, and in that the Greek Christians did not recognize the Bishop of Rome (the Pope) as the head of the universal (Catholic) Christian Church. The Greek Church had strong ties to the Byzantine Empire, which spread the faith across the former Western Roman Empire during Justinian I's reconquests in the mid-6th century AD. During the 10th century AD, the term "Greek Christian" fell out of use as Slavs and other peoples adopted the faith, and Greek Christianity is now known as "Eastern Orthodoxy" (while the Greek Orthodox Church is the church for ethnically-Greek Christians).