For the first few centuries, the Romans were constantly at war with their neighbors and therefore valued valor, both military and civil, above all else. Their poets praised not the male beauty, but the exploits of heroes.
By the 1st century BC Rome occupied all of Italy, but most importantly, it fought much less and traded much more. If previously a brutal warrior, powerful and bearded, was considered an ideal, now the Romans came to a different understanding of male beauty.
They, like the Greeks, began to prefer slender youths and clean-shaven men with an athletic build, but with the rise of individuals with political power who were not perfect in face and body, many portraits from the Roman era became surprisingly realistic, depicting signs of old age, scars and other physical imperfections. Wealth and power were positioned as the new beauty.
However, Christianity, which came in the last years of the Roman Empire, taught people the idea that nudity was shameful. On the other side, the body of Jesus Christ was supposed to be perfect since he was the son of God. Therefore, an ideal man was not a muscular or intellectual man like he was during antiquity, but someone representing spiritual perfection.