Gladiatorial combat was just a drop in the bucket. A single Roman mining operation in Spain [1] had tens of thousands of slaves working to death. Even the famous slave revolt of Spartacus ended with the spectacle of 6000 slaves crucified along the Appian Way [2].

1. https://en.wikipedia.org/wiki/Las_M%C3%A9dulas

2. https://en.wikipedia.org/wiki/Appian_Way#The_crucifixion_of_...