Answer:
Large population centers, or urban areas (1), allow civilizations to develop, although people who live outside these urban centers are still part of that region’s civilization. Rural residents of civilizations may include farmers, fishers, and traders, who regularly sell their goods and services to urban residents.
The huge urban center of Teotihuacan, in modern-day Mexico, for example, had as many as 200,000 residents between 300 and 600 CE. The development of the Teotihuacano civilization was made possible in part by the rich agricultural land surrounding the city. As land was cultivated, fewer farmers could supply more food staples, such as corn and beans, to more people.
Trade also played a part in Teotihuacan’s urban development. Much of the wealth and power of Teotihuacan was due to excavating and trading the rich deposits of obsidian around the city. Obsidian is a hard volcanic rock that was highly valued as a cutting tool. Teotihuacano merchants traded (exported) obsidian to surrounding cultures in exchange for goods and services imported to Teotihuacano settlements.
