Art of the Roman Empire hearkened back to the Classical art of the past.  “Classical” when used in reference to Roman art refers broadly to the influences of Greek art. Classical elements include the smooth lines, elegant drapery, idealized bodies, natural forms and balanced proportions that the Greeks had perfected over centuries of practice.

Look at the statue below of Augustus. You can see that this looks much more formal and idealized than the head of the old man which you just looked at. He would have been quite old (like Prime Minister Paul Martin) yet he is represented as youthful, idealized and strikingly handsome like a young athlete.

 
During the later Roman Empire, we see art looking even more formal with stiff poses, lots of drapery, and deeply cut lines. The subjects were made to look more like gods and less like real people. Important figures are often slightly larger or are placed above the rest of the crowd to show importance.

Look at the marble relief below which shows emperor Septimius Severus and his sons riding in a chariot. The faces are damaged which makes it hard to read, but you can see that they all look similar and all strike the same poses. They are all dressed the same with similar deep lines in their draped clothing. We have a hard time imagining that this is what they really looked like at the time. It is more of an idea of the scene than a true representation.