Hagia Sophia stands as one of the most significant landmarks in Orthodox Christian history. Built under Emperor Justinian I in the sixth century, it served as the spiritual heart of the Byzantine Empire and the principal cathedral of Constantinople for nearly a thousand years. Its magnificent dome, sacred mosaics, and rich liturgical tradition influenced Orthodox worship throughout the Christian world. As highlighted by the Greek Orthodox heritage sites of Istanbul, Hagia Sophia remains a powerful symbol of faith, culture, and resilience, connecting modern visitors with centuries of Orthodox Christian history and devotion.