Peoples of ancient civilizations often built their cities on the shores of natural harbors. A harbor is place on the coastline that is protected from the full effects of tide and currents (a steady flow of ocean waters in a prevailing direction). Harbors are often shaped like horseshoes. They are surrounded by land with a narrow opening through which ships can pass. Man-made harbors use structures such as walls or barriers built into the water to protect anchored ships from tide or storm damage.

Building cities near harbors permitted the construction of ports for trade. A port is a place on a shoreline for the loading and unloading of cargo from shipping vessels. Ports can be located on the ocean coast or on the shores of lakes and rivers. Cities with working ports are also called seaports or port cities.

Many of the great...