The memorial came from a 1919 attempt by Indianapolis to lure the new American Legion, which was then in New York City, to base its national headquarters in the city.
The original plaza is five blocks long. The focal point, the Indiana World War Memorial, sits on the fourth block and is modeled after the Mausoleum of Halicarnassus. It houses a military museum and an auditorium.
In 1994 the plaza became a National Historic Landmark District. In 2016 the district was expanded to include the Soldiers' and Sailors' Monument. Together it covers 24 acres, which Wikipedia says makes it the largest war memorial project in the United States.