The Catholic Church is a communion of churches. It is made up of churches from the Eastern Tradition and the Western Tradition. Eastern Catholics are in union with Rome. We share the same basic faith and the same mysteries (sacraments), however, our way of expressing them follows the same tradition as the Orthodox churches. In reality, there are many Eastern churches, each with its own heritage and theology, liturgy and discipline.
Jesus sent his disciples to the four corners of the world to spread the Gospel. Eventually, four great centers of Christianity emerged with distinctive Christian customs, but the same faith. These centers were Jerusalem, Antioch, Rome and Alexandria. A few centuries later when the capital of the Roman Empire was moved to the Eastern city of Byzantium, later renamed Constantinople, an adaptation of the Antioch celebration of the liturgy was made.
From this powerful cultural center the Byzantine church emerged.
A Brief Explanation of the Eastern Catholic Churches, Introduction)