The Piasa or Piasa Bird is a creature from Native American mythology depicted in one of two murals painted by Native Americans on cliffsides above the Mississippi River. Its original location was at the end of a chain of limestone bluffs in Madison County, Illinois, at present-day Alton, Illinois. The original Piasa illustration no longer exists; a newer 20th-century version, based partly on 19th-century sketches and lithographs, has been placed on a bluff in Alton, Illinois, several hundred yards upstream from its origin. The limestone rock quality is unsuited for holding an image, and the painting must be regularly restored. The original site of the painting was on lithographic limestone, which was quarried away in the late 1870s by the Mississippi Lime Company.

Alton is a city on the Mississippi River in Madison County, Illinois, United States, about 18 miles (29 km) north of St. Louis, Missouri. The population was 25,676 at the 2020 census. It is a part of the River Bend area in the Metro-East region of the Greater St. Louis metropolitan area. It is famous for its limestone bluffs along the river north of the city, as the former location of the state penitentiary, and for its role preceding and during the American Civil War. It was the site of the last Abraham Lincoln and Stephen Douglas debate in October 1858. The former state penitentiary in Alton was used during the Civil War to hold up to 12,000 Confederate prisoners of war. Also, the tallest man in history, Robert Wadlow, was born and raised in Alton.