Hagia Sophia, HAY ee uh soh FEE uh, is the most impressive surviving example of Byzantine architecture. Built between A.D. 532 and 537 as the Christian cathedral of Constantinople (now Istanbul, Turkey), Hagia Sophia is renowned for its huge central dome and richly decorated interior. The Byzantine emperor Justinian I ordered the cathedral built after a fire had destroyed an earlier church that stood on the site. Hagia Sophia is a Greek phrase that means holy wisdom.