In a traditional sense, Istanbul is not a city of neighborhoods. With nearly 3,000 years of continuous habitation, the only constant has been people's desire to live there. Wars, invasions, occupations, and the systematic destruction of the city, as well as plagues, devastating earthquakes, and fires, have forced residents to rebuild Istanbul many times over. Somehow, through all the remarkable changes, the remains of ancient buildings and monuments still stand today. Old Istanbul remains a walled city. A close inspection of the walls explains how the city remained invulnerable to so many attacks. In some places, the walls are 9 meters (30 feet) high and 5 meters (16 feet) thick, with 18-meter (60-foot) towers every 55 meters (180 feet).
Two bridges cross over the Golden Horn and connect old Istanbul with Beyoglu, which is characterized as "modern Istanbul." Since the eleventh century, Beyoglu has been considered the foreign quarter. This area is made up mostly of post-nineteenth-century buildings. Earthquakes, fires, and warfare just about destroyed everything before that date. Beyoglu is divided into two sections: the lower Galata water-front and the Pera Plateau, home to consulates and Turkish government offices, as well as many of the city's largest hotels and best restaurants. The city reaches across the Bosporus to its Asian side with two bridges, one completed in 1973 and the other in 1988.
Housing is a problem in Istanbul; occupancy rates hover at about 13 persons per unit. As migrants, especially from the Asian side of Istanbul, have moved into the city, large shantytowns have appeared throughout the metropolitan area.