Istanbul is in north-western Turkey within the Marmara Region on a total area of 5,343 square kilometers (2,063 sq mi).
The Bosphorus, which connects the Sea of Marmara to the Black Sea, divides the city into a European, Thracian side—comprising the historic and economic centers—and an Asian, Anatolian side.
The city is further divided by the Golden Horn, a natural harbor bounding the peninsula where the former Byzantium and Constantinople were founded.
The confluence of the Sea of Marmara, the Bosphorus, and the Golden Horn at the heart of present-day Istanbul has deterred attacking forces for thousands of years and remains a prominent feature of the city's landscape.

Following the model of Rome, the historic peninsula is said to be characterized by seven hills, each topped by imperial mosques.
The easternmost of these hills is the site of Topkapı Palace on the Sarayburnu.
Rising from the opposite side of the Golden Horn is another, conical hill, where the modern Beyoğlu district is.
Because of the topography, buildings in Beyoğlu were once constructed with the help of terraced retaining walls, and roads were laid out in the form of steps.
Üsküdar on the Asian side exhibits similarly hilly characteristics, with the terrain gradually extending down to the Bosphorus coast, but the landscape in Şemsipaşa and Ayazma is more abrupt, akin to a promontory.
The highest point in Istanbul is Çamlıca Hill, with an altitude of 288 meters (945 ft).
The northern half of Istanbul has a higher mean elevation compared to the south coast, with locations surpassing 200 meters (660 ft), and some coasts with steep cliffs resembling fjords, especially around the northern end of the Bosphorus, where it opens up to the Black Sea.

Istanbul is near the North Anatolian Fault, close to the boundary between the African and Eurasian Plates.
This fault zone, which runs from northern Anatolia to the Sea of Marmara, has been responsible for several deadly earthquakes throughout the city's history.
Among the most devastating of these seismic events was the 1509 earthquake, which caused a tsunami that broke over the walls of the city and killed more than 10,000 people.
More recently, in 1999, an earthquake with its epicenter in nearby İzmit left 18,000 people dead, including 1,000 people in Istanbul's suburbs.
The people of Istanbul remain concerned that an even more catastrophic seismic event may be in the city's near future, as thousands of structures recently built to accommodate Istanbul's rapidly increasing population may not have been constructed properly.
Seismologists say the risk of a 7.6-magnitude or greater earthquake striking Istanbul by 2030 is more than 60 percent.
Istanbul is in north-western Turkey within the Marmara Region on a total area of 5,343 square kilometers (2,063 sq mi). The Bosphorus, which connects the Sea of Marmara to the Black Sea, divides the city into a European, Thracian side—comprising the historic and economic centers—and an Asian, Anatolian side. The city is further divided by the Golden Horn, a natural harbor bounding the peninsula where the former Byzantium and Constantinople were founded. The confluence of the Sea of Marmara, the Bosphorus, and the Golden Horn at the heart of present-day Istanbul has deterred attacking forces for thousands of years and remains a prominent feature of the city's landscape.
Following the model of Rome, the historic peninsula is said to be characterized by seven hills, each topped by imperial mosques. The easternmost of these hills is the site of Topkapı Palace on the Sarayburnu. Rising from the opposite side of the Golden Horn is another, conical hill, where the modern Beyoğlu district is. Because of the topography, buildings in Beyoğlu were once constructed with the help of terraced retaining walls, and roads were laid out in the form of steps. Üsküdar on the Asian side exhibits similarly hilly characteristics, with the terrain gradually extending down to the Bosphorus coast, but the landscape in Şemsipaşa and Ayazma is more abrupt, akin to a promontory. The highest point in Istanbul is Çamlıca Hill, with an altitude of 288 meters (945 ft). The northern half of Istanbul has a higher mean elevation compared to the south coast, with locations surpassing 200 meters (660 ft), and some coasts with steep cliffs resembling fjords, especially around the northern end of the Bosphorus, where it opens up to the Black Sea.
Istanbul is near the North Anatolian Fault, close to the boundary between the African and Eurasian Plates. This fault zone, which runs from northern Anatolia to the Sea of Marmara, has been responsible for several deadly earthquakes throughout the city's history. Among the most devastating of these seismic events was the 1509 earthquake, which caused a tsunami that broke over the walls of the city and killed more than 10,000 people. More recently, in 1999, an earthquake with its epicenter in nearby İzmit left 18,000 people dead, including 1,000 people in Istanbul's suburbs. The people of Istanbul remain concerned that an even more catastrophic seismic event may be in the city's near future, as thousands of structures recently built to accommodate Istanbul's rapidly increasing population may not have been constructed properly. Seismologists say the risk of a 7.6-magnitude or greater earthquake striking Istanbul by 2030 is more than 60 percent.
Istanbul