Greek settlers from Megara founded Byzantium on this peninsula around 660 BCE. The site they chose, where the Bosphorus meets the Sea of Marmara, controls the only sea route between the Black Sea and the Mediterranean, and the city has lived off that geography ever since. In 324 CE, Constantine the Great chose the same spot to build a new Christian capital for the Roman Empire. He renamed it Nova Roma, but everyone called it Constantinople. On May 11, 330, it was formally proclaimed capital of the empire. For the next eleven hundred years, Constantinople was the seat of what we now call the Byzantine Empire and, on multiple counts, the largest and richest city in Europe. Then on May 29, 1453, after a 55-day siege, Sultan Mehmed II broke through the walls. The last Roman emperor, Constantine XI, died fighting in the streets. Mehmed renamed himself Kayser-i Rum, Caesar of Rome, and the city's third long chapter began.

Hagia Sophia is the oldest of the great domes and shaped everything that came after. Justinian I completed it in 537, and for nearly a thousand years it was the largest cathedral in the world. The dome is 31 meters across and seems impossibly weightless from inside, an effect produced by the ring of windows at its base. After 1453 it became a mosque, then a museum in the secular Republic, and in 2020 a mosque again. The Ottoman architects who came later, especially Mimar Sinan in the 16th century, built their imperial mosques in dialogue with it. The Süleymaniye, finished in 1557, is Sinan's answer. The Sultanahmet Camii, the Blue Mosque, finished in 1616, is the next century's response. Walk the historic peninsula and you walk through that long architectural conversation, building by building.

Istanbul does not have a single primary park, but it has the Bosphorus, which functions as the city's spine. Ferries cross constantly between the European and Asian shores; the morning commute is one of the more beautiful in the world, with seagulls riding the wakes for thrown bread and the hills of Üsküdar lighting up across the strait. Three suspension bridges now span the Bosphorus, the first opened in 1973. The Marmaray rail tunnel, opened in 2013, runs beneath it. And then there are the cats. Tens of thousands of free-roaming cats live in Istanbul, fed at corner shops and curled in mosque courtyards, and they have become one of the city's most affectionate identifiers. A 2016 documentary called Kedi made them internationally famous, but the cats predate the documentary by centuries.

Behind the Beyazıt Mosque, in a small courtyard reached by a narrow gate, sits the Sahaflar Çarşısı, the secondhand book bazaar. There has been a book market on or near this spot since the Byzantine era. The current bazaar, with its cluster of shaded stalls under plane trees, dates in its present form to the 1950s. You can find Ottoman calligraphy, Republican-era textbooks, French novels left behind by the Levantines, and recent paperbacks stacked to the ceiling. A few hundred meters away is the Grand Bazaar, with its 4,000 shops under vaulted Ottoman ceilings, founded in 1461 by Mehmed II. A few hundred meters in another direction is the Spice Bazaar, founded in 1664 to fund the Yeni Mosque. The historic commercial fabric of the city is still doing business.

The growth has come at a cost. The North Anatolian Fault runs just south of the city, and Istanbul has been hit by major earthquakes throughout its history, most recently a magnitude 6.2 quake on April 23, 2025. Geologists expect another large rupture in the 21st century. Since 2012, more than 500,000 buildings deemed seismically vulnerable have been demolished and replaced. Air pollution remains acute, and the Sea of Marmara has experienced major algal blooms and a 2021 marine mucilage crisis. The Greek population, which numbered 110,000 in 1919, is now around 2,500, the result of the 1942 wealth tax, the 1955 pogrom, and the 1964-65 expulsions. The city's history is layered, but not all the layers have been protected equally.