Istanbul is an architectural palimpsest: spectacular traces from the past endure in the contemporary urban fabric. Over 16 centuries it served as capital for the Byzantine and Ottoman empires, successively. When it changed hands in the 15th century, Sultan Mehmet II did not indiscriminately raze Byzantine monuments; rather, recognizing their tremendous cultural value, he adapted them to serve his new empire. The Haghia Sophia, Istanbul's most enduring monument, has been both Byzantine church and Ottoman mosque. Under the Turkish Republic it was transformed into a museum, the modern, secular equivalent of a house of worship; the main artifact on display is the building itself. As Turkey approaches another threshold, negotiating its entry into Europe, this time-honored strategy of architectural reuse is reemerging as industrial relics from the late Ottoman period are refashioned into modern and contemporary art institutions like the Istanbul Modern and the Santral Istanbul.