Rory Calhoun, who was in Italy for the title role in MGM's Marco Polo, stepped into the lead role of "Colossus" on only one day's notice. He initially arrived at 11:30 on the first day he was to start filming. According to Leone biographer Christopher Frayling, Calhoun's first day included an accidental fall into a swimming pool.
According to Sir Christopher Frayling, Sergio Leone's early concept for the Colossus was to have its arms crossed and the visage of Benito Mussolini. This concept was abandoned and replaced with Helios/Apollo.
Although he had experience directing other films, this was the first to give full on-screen credit to Sergio Leone.
During most of his scenes, Rory Calhoun wears a wide bracelet on his left arm and stiffly extends it covered by a cloak. According to Sergio Leone scholar Christopher Frayling and Calhoun's widow, the actor did that to hide some 20th-century tattoos.
Metro-Goldwyn-Mayer's U.S. trailer mentioned that 'Rory Calhoun' was the star of the television series The Texan.
One of the few films to be set in the Hellenic period that spanned the period from the death of Alexander the Great to the rise of Rome as a world power.
The credits of the U.S. release version lists four screenwriters. The screenplay was reportedly the work of nine screenwriters.
The English language versions of "Colossus" refer to the Athenian hero Darios by the Italian version of his name, Dario.
The original choice for the role of Darios was John Derek, who had played a similar role a few years earlier in The Ten Commandments.
The real Colossus, one of the Seven Wonders of the Ancient World, was 32 meters high and stood on a hill. The cinematic version stands 110 meters and its legs bestride the harbor.
The widescreen process used is TotalScope, an Italian version of Cinemascope.