Rome's dominant society was originally Etruscan. This style of art, similar to greek Archaic, heavily influenced early Roman sculpture. Romans were very fond of Greek sculpture and would make copies. It is actually thanks to this that we still know of some great works. However, Romans added an element of realism to their sculpture that was simply not present in Greek works. The works were still used in the same ways, though. Sculptures reprenting leaders would be placed in public locatons to show respect and power. This could be in the form of busts, sculptures, or low-relief carvings. These carvings could be placed on huge arches or towers.
Trajan's Column is a huge Roman monument honouring, of course, Trajan. It is an example of a spiral frieze. Normally, a frieze is located on the entablature of a building, but in this case, the entire column is a frieze. It spirals the whole way up, telling stories of military victories as it goes. Curiously, most of it is completely unreadable, especially for those living in ancient times. Though a staircase exists inside, it still is still not possible to read the middle parts. The top of the structure originally may have had a sculpture of a bird, which was then replaced by a statue of Trajan. This, too, disappeared at some point in the Middle Ages. Finally, in 1588, St. Peter's likeness was placed at the top and it remains to this day.
Another famous low-relief carving is the Ara Pacis. This is thought to be one of the most important works of its kind from this time. The detailed frieze shows different images, all of which show peace or the process of peace.
Realism, once very prominant in sculpture, begins to slip away as Christianity changes things up. Sculptures for the next millenium become extremely symbolic and tend to be more low-relief as opposed to sculptures in the round. Powerful, strong figures are replaced by less sure ones.