Why did some native american groups build mounds?

The various cultures collectively termed "Mound Builders" were inhabitants of North America who, during a circa 5,000-year period, constructed various styles of earthen mounds for religious, ceremonial, burial, and elite residential purposes

operation overlord was the codename for the battle of normandy, the allied operation that launched the successful invasion of german-occupied western europe during world war ii. the operation was launched on 6 june 1944 with the normandy landings