Final answer:
Cahokia was a preeminent pre-Columbian mound-building city that is considered a significant chiefdom, known for its large population, advanced societal structure, and extensive trade networks.
Step-by-step explanation:
Cahokia was an impressive pre-Columbian Native American city that emerged around AD 1050 near what is today East St. Louis. It is renowned for its complex of 120 mounds, the largest being Monk's Mound, which is about ten stories high. These mounds served various functions, including ceremonial, burial, and possibly residential uses for the elite. Cahokia was a significant urban center with a population possibly reaching 30,000 at its peak, and it featured advanced structures such as a woodhenge used for astronomical observations. It is also noted for its vast trade networks and the role it played as a regional hub for political and trading activities. Its decline began around 1300 CE due to various speculated factors such as overhunting, deforestation, and the emergence of competing centers like Moundville.