Muscular black men could be found in peplum movies from the very start. Usually as gladiators or slaves. Remember Maciste was originally a black man. Though he was played by white actor/strongman Bartolomeo Pagano with his skin cosmetically darkened. His first screen appearance was in the 1914 silent film epic CABIRIA based on the historical novel Salammbo by Gustave Flaubert. In all subsequent films he was portrayed as caucasian. And that would be the case in all the Maciste movies from the sinew & sandal movie cycle from the 50s and 60s.
In gladiator movies you might find a black man playing the hero's best friend and confidant as William Marshall did in the 1954 Hollywood epic DEMETRIUS AND THE GLADIATORS. In the muscleman flicks like the SON OF HERCULES VS. THE MOLE-MEN you might find a black man as the hero's sidekick. Former Mr.Universe Paul Wynter filled the bill in that flick. Harry Baird played a similar role in the flicks TAUR THE MIGHTY and THOR AND THE AMAZON WOMEN. And then there was Serge Nubret.