However, the attraction's website describes the Cyclorama as follows:
The Cyclorama of the Battle of Atlanta is the world's largest oil painting, painted in 1885-86 by artists from Germany. It has been shown in Grant Park since 1893.
The three-dimensional foreground, called a diorama, was added in 1936, bringing a depth of 30 feet to the display.
Here is a great photo from this site:
This a great photo of Clark Gable and Vivian Leigh touring the exhibit in 1939:
Finally, this is a unique news clip that shows how volunteers care for "the world's most bizzare tourist attraction":