Answer: Mississippian
The Mississippian culture was a Native American civilization that flourished in what is now the Midwestern, Eastern, and Southeastern United States from approximately 800 CE to 1600 CE, varying regionally. It was known for building large, earthen platform mounds, and often other shaped mounds as well.
Explanation:
Because rusting make the steel's structural strength became weak.
In construction, we use steel as a foundation that hold the building's structure. If we don't guard against the rusting of steel, we will expose the building to a very high potential risk of collapse