I arrived in Istanbul early in the morning, on the ferry from the European port to the Asian port — a twenty-minute crossing of the Bosphorus that never stops being strange, even on the fourth or fifth time. The strait is narrow: you see both shores at once, minarets on one side, skyscrapers on the other, Russian freighters and commuter ferries crossing paths. There is no other point on earth where the concept of “border” is physically so immediate and so porous at the same time.
Istanbul was Constantinople for eleven centuries, capital first of the Eastern Roman Empire and then of the Ottoman Empire. Every great building here has passed through at least two existences: Hagia Sophia was a Christian church for nine hundred years, then a mosque for five hundred, then a museum for eighty-six, then a mosque again. The Chora, the Temple of Peace, the Cisterns — every structure carries in its own matter the traces of every function it has served. Istanbul is stratification as a permanent condition, not as a historical exception.
Hagia Sophia — the dome that changed everything
The first time you enter Hagia Sophia — today a mosque again, with carpets covering the marble floor and some Christian images veiled — something unexpected happens: the space is larger than the outer façade suggested. Not because the dimensions deceive — the central dome has a diameter of 31 metres and a height of 55 metres — but because the system of semi-domes flanking the main dome creates a series of lateral expansions that widen the perceived space in all directions. You are not in a room under a dome: you are in a landscape of domes.
The structural ingenuity of the architects Anthemius of Tralles and Isidore of Miletus, who built it for Justinian between AD 532 and 537, lies in the management of thrusts. A dome pushes outward: if you do not contain that thrust, the walls give way. At Hagia Sophia the thrust is absorbed by the lateral semi-domes, then by smaller apses, then by buttresses. The system is a cascade — each element transmits and absorbs part of the load. The result is that the walls can be opened by windows: at the base of the dome there are forty windows that at certain moments of the day make the dome seem suspended in the air, detached from the walls.
The building system and its impact on later Islamic architecture: Islamic architecture — geometry as revelation.
The Blue Mosque — the system of semi-domes
The Blue Mosque stands opposite Hagia Sophia, built by Sultan Ahmet I between 1609 and 1616. The design is by the architect Sedefkâr Mehmed Ağa, a pupil of the great Sinan. The stated aim was to build something that could converse with Hagia Sophia — and the dialogue happens through the same structural system: a central dome (23 metres in diameter) supported by four semi-domes, which in turn rest on smaller apses. It is a matryoshka system of masonry structures that distributes the loads toward the four massive piers of the prayer hall.
The Turkish name — Sultan Ahmed Camii — is more correct than “Blue Mosque”, which refers to the 20,000 blue ceramic Iznik tiles that line the interior. But here too the detail reveals the method: the tiles are not only decoration, they are the way the light filtered from outside — twenty-eight windows in the dome, a hundred windows in the walls — is distributed and amplified inside. Ceramic reflects. The space lights up from within, not only from outside.
The Grand Bazaar — Ottoman commercial architecture
The Grand Bazaar is not a building in the conventional sense: it is a city within the city. Over 4,000 shops, 61 covered streets, some of which date from the fifteenth century under the Ottomans. Architecturally, what is worth observing is the system of bedestens — the original cores of the bazaar, large covered halls with masonry groin vaults where valuable goods were kept. The oldest bedesten, the Cevahir (or İç) Bedesteni, has domes from 1461; the Kalpakçılar, by contrast, is the bazaar's main street. All around, over five centuries, the bazaar has grown organically — like a medieval city, without a master plan, by progressive addition of shops, covered alleys, fountains, small mosques.
The result is one of the most complex urban spaces I know: no point has the same height as the previous one, no alley is perfectly straight, the light varies continuously. You cannot tell where the centre is — there is none. It is a labyrinth that works perfectly because over time it has found its own organic balance.
Istanbul Modern — the contemporary on the Bosphorus
Istanbul Modern moved in 2023 to a new building designed by Renzo Piano Building Workshop, on the Karaköy waterfront. It is a building of glass and steel looking directly onto the Bosphorus — one of the few contemporary buildings in the city with a direct relationship with the water. Piano uses transparency as a tool of connection: from inside the museum you see the port, the ferries, the Asian side of the city. The artworks converse with the urban landscape as a backdrop.
In such a dense historical context, the contemporary museum does not try to compete with Hagia Sophia or with the mosques of the Golden Horn. It chooses a different register — lightness, transparency, horizontal instead of vertical — and works as counterpoint rather than confrontation.
The city that remains
Istanbul is the only city I know in which the problem of cultural syncretism is solved by the buildings themselves. Not by speeches, not by policies, by buildings. Hagia Sophia carries in its space the history of Christian Rome and of Ottoman Islam and of the secular Turkey of the twentieth century — all together, in the same walls, in the same reused marble and porphyry columns, salvaged from ancient buildings across the empire. There is no synthesis: there is stratified coexistence.
When you are inside Hagia Sophia during Friday prayer, with the faithful in rows on the carpets and the Christian mosaics half visible beyond the veils, you understand that the city has never needed to choose. It has contained everything, as its buildings contain everything — layer on layer, function on function, time on time.