The peninsula is roughly rectangular. It is bordered by the Black Sea to the north, Sea of Marmara to the South and Bosphorus to the east. The west border is more or less arbitrary. But usually the western border of İstanbul Province is also taken as the border of the peninsula . With these borders, the north to south dimension is about 40 kilometres (25 mi) and the west to east dimension is about 90 kilometres (56 mi). Çatalca Peninsula is almost a duplicate of Kocaeli Peninsula on the other side of Bosphorus. In fact, the geographers consider it to be a part of Kocaeli Çatalca subregion. There are several natural and artificial lakes in Çatalca peninsula including Lake Durusu, Lake Büyükçekmece and Lake Küçükçekmece.
During the reign of Byzantine Emperor Anastasius I (491-518) a defense wall had been constructed between Evcik beach at the north and Silivri at the south to defend İstanbul (then known as Constantinople) from Huns and other attackers. The 40 kilometres (25 mi) wall was one of the longest ramparts of Europe. But even then such attackers as Avars (616), Bulgarians (813) and Pechenegs (1090) were able to lay siege to İstanbul. After 1371, most of Çatalca Peninsula fell to Ottoman Turks. The whole peninsula became a part of Ottoman Empire by the conquest of İstanbul in 1453. Since then Çatalca Peninsula is a Turkish land except for Bulgarian attack during the first Balkan war and temporary occupation by Greece at the end of the First World War.
The population and the economy
Çatalca Peninsula (together with Kocaeli Peninsula at the other side of Bosphorus) is the most industrialised region of Turkey. Approximately two thirds of İstanbul, one of the most populous cities of the world with 13.120.596 inhabitants  constitute the population of Çatalca Peninsula . The population density of the peninsula exceeds 2000/km2 (5180/ mi2).