How far back can we trace the intentional training of strength and body building? We often see images of huge gladiators and warriors with huge muscles, but would this be from training or purposefully doing exercises to increase specific muscles? How precise were these exercises?
I don't know for sure, but gladiators in the arena intentionally built muscle and then a layer of subcutaneous fat by eating a vegetarian diet rich in carbohydrates and low in protein, so they could sustain impressive-looking yet non-fatal injuries. They looked like a cross between sumo wrestlers and WWE wrestlers. Source.
So most of our idealized modern versions of gladiators aren't accurate. They were concerned with their body size and shape, but not in the way we think they would be.
For most of history, the ideal body for a man was stocky and core-strong, which is different from the idealized Western triangle-shaped upper torso.
A previous answer I gave on the history of modern weightlifting. Might help you out.