MGM FX Department:

Special  Photographic effects: Robert R. Hoag  / A. Arnold Gillespie / Cliff Shirpser
Matte painting supervisor:  Lee LeBlanc
Matte artist: Matthew Yuricich
Special effects: Robert MacDonald
 

The real set without the painting

Matte painter Mat Yuricich at work.

Two behind the scenes images of the  set built at Cinecitta, Rome.