Isn't it more likely they were vegetarians not by choice but because they were essentially slaves, being fed the cheapest food possible (grains, etc)?

Though I'm sure many will use this as evidence in favor of vegetarianism... "Yeah but even the mighty gladiators were vegans!"

Anecdote storytime; I was actually born and raised into a vegetarian household, and spent the first approx 22 years of my life as a vegetarian. Then I switched to eating meat (really, just chicken and fish, maybe red meat once a year) and for me I feel healthier this way. When eating meat I can just eat less total volume of food to get the same amount of calories and nutrients compared to fueling up on a plant based diet. I love running, hiking and rock climbing, and nothing quite hits the spot like a nice protein rich chicken sandwich after a day in the mountains. YMMV, but for me, for now, I think I will continue with my consumption of animal flesh. I think to pull off the veg diet you have to carefully measure and monitor things, you can't just omit entire food groups from your diet and expect to be healthy. It's very naive but many vegan and vegetarians think this way; As long as the food has that VeganTM label, it must be good, why bother even checking the ingredients?

Tldr; ex-vegetarian since birth prefers chicken sandwiches for climber fuel