The single most astonishing building in Istanbul, and arguably the most consequential in the history of architecture. Emperor Justinian raised it as a cathedral in 537, its dome so wide and shallow that for a thousand years nothing rivalled it; the Ottomans made it a mosque in 1453 and added the minarets, and after decades as a museum it returned to working-mosque status in 2020. It remains a UNESCO World Heritage Site. Inside, the sheer scale stops people mid-step, and the surviving gold Byzantine mosaics of Christ, the Virgin and the emperors glimmer high on the walls above Islamic calligraphic roundels, a rare overlay of two faiths in one space. Tourists now enter through the upper gallery, where the best mosaics and the famous dome views are found. Come at opening to beat both the crowds and the heat, dress modestly, and steer well clear of Friday midday prayers.
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