Why Most Megacities Form Around Rivers – and the Unique Case of Mexico City

Throughout human history, rivers have served as the natural foundation for urban development. Nearly every major city—ancient or modern—owes its origins to the advantages provided by proximity to a river. Yet one extraordinary exception stands out: Mexico City. Unlike most megacities, Mexico City developed and continues to thrive without a natural river flowing through it. Understanding this contrast reveals how geography, technology, and history shape the patterns of global urbanization.

Rivers as the Cradle of Civilization

Rivers have historically provided the essential conditions for settlement:

  • Water supply: Early cities required constant access to fresh water for drinking, irrigation, and sanitation.

  • Agriculture: Floodplains around rivers are fertile due to nutrient-rich sediments, enabling stable food production.

  • Transportation: Before railways and highways, rivers functioned as natural trade routes, connecting inland settlements to larger markets.

  • Energy and industry: Flowing water powered mills and later served as a cooling and waste outlet for industries.

For these reasons, cities like Cairo (Nile), Paris (Seine), Shanghai (Huangpu), and Delhi (Yamuna) emerged where rivers offered both life and commerce. As populations grew, these settlements evolved into modern megacities—urban areas exceeding ten million inhabitants.

Geographic and Economic Advantages

Rivers also create ideal conditions for large-scale urbanization:

  • They define flat, low-lying areas that simplify construction and infrastructure.

  • They offer strategic control points for trade, taxation, and defense.

  • They attract investment and migration, stimulating sustained growth over centuries.

Thus, the presence of a river has been not just a convenience but a structural driver of megacity formation.

The Exceptional Case of Mexico City

Mexico City defies this pattern. Located in a closed highland basin at over 2,200 meters above sea level, it was built on what was once a system of interconnected lakes rather than a river plain. Its pre-Columbian predecessor, Tenochtitlán, was founded by the Aztecs in 1325 on islands within Lake Texcoco. The city thrived through an intricate network of canals, causeways, and dikes—essentially a hydraulic civilization without rivers.

When Spanish colonizers conquered the region in the 16th century, they sought to control the frequent flooding of the valley. Over centuries, they drained the lakes, diverted the streams, and filled in the canals, transforming a lacustrine ecosystem into a dry basin. Today, no natural river flows through Mexico City; water is imported from distant sources via massive aqueducts, while excess rainwater is expelled through deep drainage tunnels.

Consequences of an Artificial Hydrology

The transformation of the Valley of Mexico brought major challenges:

  • Water scarcity: Groundwater over-extraction has caused the city to sink by several centimeters per year.

  • Flood risk: The absence of natural drainage makes heavy rainfall catastrophic.

  • Ecological loss: Only remnants of the original lake system remain, most notably in Xochimilco.

Despite these problems, Mexico City remains one of the world’s largest metropolitan areas, home to over 20 million people—proof that human engineering can substitute for natural geography, but often at a steep environmental cost.

    Rivers have historically dictated where cities could exist and how they could grow. They offered water, transport, and fertile land—the foundation of civilization. Mexico City stands as a striking exception: a megacity sustained not by a river’s gifts, but by technological adaptation to an environment it radically transformed. Its story underscores both humanity’s ingenuity and the long-term risks of ignoring natural hydrological systems in urban planning.




Vincent
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