İstanbul was established at B.C. 7th century. The part of İstanbul that surrounded by Haliç in north, Bosphorus in east and Marmara Sea in South is being mentioned as “Historical Peninsula” in present day. City has been so important for the civilizations ruling upon due to İstanbul's trategic location that connects Europe and Asia. With these properties, İstanbul has been  capital city for great empires like Roman Empire, Eastern Roman Empire and Ottoman Empire. 

İstanbul was included in UNESCO World Heritage List as 4 districts at 1985 with its glorious past, and properties that bringing different religions, cultures, societies and objects produced by those in a unique geography. Those districts are Sultanahmet Archaelogical Urban Site including Hippodrome, Hagia Sophia, Hagia Irene, Little Hagia Sophia Mosque and Topkapı Palace, Süleymaniye Conservation Area including Süleymaniye Mosque and surroundings, Zeyrek Conservation Area including Zeyrek Mosque and surroundings and Conservation area for İstanbul Land Walls.

https://kvmgm.ktb.gov.tr/TR-44425/istanbulun-tarihi-alanlari.html
http://www.alanbaskanligi.gov.tr/miras_alani_siniri.html