I am guessing that there is a series of "Son of Hercules" movies: the theme for this movie is the exact same as that of "Son of Hercules vs. the Fire Demon."
A montage of corpses are shown as a chorus of men sing "The mighty sons of Hercules are men as men should be! They took the world and kept the world the sons of Hercules!" Not exactly Shakespeare but hey...at least it's got a groovy beat you can dance to.
The narrator informs us this film recounts the adventures of Glaucus, pronounced "GLAW-cuss" (played by a well oiled Richard Harrison) and his struggle with the empress Messalina.
In 41 AD Caligula rules the land. In his pointless war against Britain (well played by the Italian countryside) Caligula watches Glaucus the Brit fight. Excited by what he sees (Caligula shows his delight by petting a cat) he takes Glaucus back with him as a slave.
Back in Rome (well played by a blurry matte painting) Caligula makes his horse a senator. Messalina, wife of Claudius, watches in horror as Caligula and his midget sidekick laugh at each new outrageous law Caligula enacts. At the Roman games Glaucus fights with obvious skill. The crowd (all 20 of them) yells in obvious pleasure, quieting down when someone makes a statement like "wow, what a man warrior!" Caligula is not impressed, however, when Glaucus throws an axe at him. Glaucus is arrested and Messalina starts a plan to use Glaucus as a means to overthrow Caligula.
This production has all the typical Italian beefcake trademarks - bad dubbing, over-acting (in some cases, under-acting), a midget, and men in loincloths. Richard Harrison may not have the biggest muscles but he certainly is the most titillating beefcake actor I've seen. And when it comes to loincloths you have to wonder why his "mini-skirt" is not mini enough. They must not have seen a good thing when they had it, and with too much loincloth neither can we.