Stallone, Arnold Schwarzenegger and Mel Gibson waved at fans from three tanks that drove slowly down the main boulevard in the French Riviera town where the international film festival is in its fifth day.
The film, which is not in competition, also features Harrison Ford, Antonio Banderas, Jason Statham, Dolph Lundgren and Wesley Snipes and the cast was asked by reporters to describe just what makes a good action star.
"You have to be incredibly intelligent, handsome, sexy, good teeth, high IQ, a lot of hair," Stallone joked.
"There's something that's almost intangible and I don't know what it is, but I know it's very rare because there have only been about 15 action heroes, real serious ones, in history."
Stallone, one of the film's writers, said it took three movies to get the 'Expendables' formula just right, judging the first as being too violent and the second too soft.
"I believe we finally got it right in the third one – kind of like marriage."
Stallone acknowledged that he and the rest of the cast belonged to a "different generation", but still had the energy and drive to make an exciting, contemporary film.
"We're all like very adult children," Stallone said. "We are children with arthritis. We are young forever."
The third instalment of the franchise sees Barney Ross (Stallone) bringing in new blood to his team of mercenaries to take on Conrad Stonebanks (Gibson), a former comrade now seeking to eradicate the group.