The architectural achievement associated with the Byzantine Empire in Constantinople is the Hagia Sophia. Completed in 537 AD under the Byzantine Emperor Justinian I, the Hagia Sophia was originally constructed as a cathedral and later converted into a mosque. Renowned for its massive dome and innovative engineering, it symbolizes the sophistication and power of Byzantine architecture. The building features intricate mosaics and a blend of architectural styles that reflect both Roman and Orthodox Christian influences. Today, the Hagia Sophia stands as a UNESCO World Heritage Site and continues to be a prominent cultural and historical landmark, illustrating the artistic achievements of the Byzantine Empire.