A large human settlement,[1] generally having extensive housing, transportation, food, sanitation, utility, land-use and communication systems. The city’s density facilitates interaction among diverse people, government organizations, institutions and businesses.

Historically, city dwellers have constituted a small proportion of humanity; however, following two centuries of unprecedented and rapid urbanization, roughly half of the world population now lives in cities and metropolitan areas, which has had profound consequences for global sustainability. Present-day cities usually form the core of larger metropolitan areas and urban areas, involving waves of daily commuters traveling into and out of city centers for employment, entertainment, education and transactions. In a world of intensifying globalization, all cities are also variously connected beyond these regions, as well as globally.

The world’s most-populated city proper is Shanghai.[2] Meanwhile the most populous metropolitan areas are Greater Tokyo, Delhi and Jabodetabek (Jakarta).[3]

The first known city in history was Uruk, in Akkadian Biritum/Birit Narim, or what the Greeks later called Mesopotamia, modern Iraq). Jericho (Palestine), Sidon (Lebanon), and even Eridu (Sumer/Iraq) were settled earlier, but lack the verifying documentation found at Uruk.[4]

The first known city in the New World was Caral, Peru.[5]

In the study of the ancient world, a city is generally defined as a large, populated urban center of commerce and administration with a system of laws and, usually, regulated means of sanitation. This is only one set of characteristics, however, and the designation of “city” can be based on such other factors as:

• Concentrated population (number of inhabitants),
• Large and/or high (multistory) buildings,
• Density of buildings/population,
• Presence of some kind of sewer system,
• Level of administrative government,
• Presence of walls and/or fortifications (by ca. 2,900 B.C.E.),
• Social heterogeneity,[6]
• Geographical area of the settlement, or
• Whether a “settlement” was called a “city” in antiquity and meets any of the above qualifications.

The cities of Faiyum (Egypt),[7] Damascus (Syria)[8] and Varanasi (India)[9] are among the cities with the longest continuous inhabitation.