The action men were pitted as rivals as their careers took off in the 1980s and they both began to believe the hype.
"Stallone and I had a major battle of who is more ripped, who has more muscles, who has more box office growth, who killed more people in the movies, who uses bigger guns and bigger and more effective knives," Arnie tells Parade.
But when they eventually met and became partners in the Planet Hollywood empire, the two stars realised they had more in common than they imagined - and they buried the hatchet by exchanging weapons.
"He gave me a knife from 'Rambo' and I gave him a knife from 'Commando', because we were laughing about how stupid (the rivalry) was," Schwarzenegger adds, "but also how necessary, because it helped me perform better. I tried to outdo him and I helped him try to outdo me."