Set in the distance future where alien had seemingly annihilated about 99% of the entire human population including space colonies, the remaining survivors are enslaved for entertainment purposes only.
Soon the alien grown bored so they created a dozen of cloned dinosaurs from the late Cretaceous period and set them to roam freely in the Roman empire via a temporal shift, these dinosaurs will appear simultaneously within a densely populated area.
Comment below should there be any doubt. I've changed from hybrid to clone so these diversity of dinosaurs are the exact copies of their originals, the only difference is the alien have somehow enables the dinosaurs to adapt to the new environment and climate.
My question is how can a battalion of Roman soldiers subdue 1 adult giganotosaurus, 1 adult spinosaurus, 1 pair of adult Tyrannosaurus Rex and 12 dozen of velociraptors during a surprise attack in the middle of the night? Kindly take note the soldiers are taken by surprise and this will be their first and probably only engagement.
Note: No worry these dinosaurs are programmed to hunt only mammals, so don't expect the people of Roman empire to watch a brawl between these ferocious creatures while betting. I'll applaud you if you can keep the human casualties within 2 digit figures within a week.