Why are St. Paul and Minneapolis called "Twin Cities"?
The term was first applied to two settlements on either side of the Mississippi River—St. Anthony's Falls on the east and Minneapolis on the west—in the 1840s.
The two towns were later linked by a suspension bridge. Minneapolis was chartered as a city in 1867 and in 1872 it and St. Anthony's Falls were united to form one city. As a result, nearby St. Paul assumed the nickname while it and the new Minneapolis grew during the 20th century to become Minnesota's two biggest cities.
—The Fact Monster