The first innovations of sculpture had already been adopted by the Etruscans who traded with the Greek colonies of southern Italy, well before Rome was a city to be reckoned with.
At the basis of Greek sculpture we can find a journey of growing consciousness of the individual and his place within the world about him. The concept of the application of proportion to the human figure (and to architecture also) are a well known achievement but we shouldn’t forget the debt owed to the Egyptians before them who likewise applied predefined proportions to their pyramids and sculptures.
If we consider the Etruscans as a sort of proto-Roman we should consider the achievement in clay figures such as the Apollo of Veii which has astonishing vitality as well as being distinctly Italic in nature. The very statue of the she-Wolf feeding Romulus and Remus kept at the Capitoline museums was forged in an Etruscan workshop under Roman commission.
Perhaps the great achievement of the Greeks is that of interpreting man in his natural surroundings: studying and analyzing to such a degree as to render proportion and then make that magical step in understanding that in order to convey movement one has to resort to a degree of distortion.
The Romans were great pragmatists where the individual was truly an individual (at least the free citizens could regard themselves as such). Sculpture was developed by the Greeks to bring the gods to human life. The Romans used sculpture increasingly as a means of glorifying the individual citizen and in later stages as a means of architectural decoration. This glorification could be self glorification through the commissioning of commemorative and sometimes monumental portraits. A good example of this is the now lost colossal statue of Nero or that of emperor Constantine, of which a number of pieces are still visible. Alternatively the individual could pride himself in his collection of sculptures which were relatively commonplace in the gardens of the villas of the rich and mighty.
These sculptures were not necessarily “originals”: the Romans had learned the practice of creating replicas. Plaster casts were made of the great original masterworks (of the Greeks) and these could be shipped to every corner of the Roman empire to be reproduced and then copied to marble by more or less able hands. By this means a great many Roman marble replicas of ancient Greek originals have made it our museums. Often the originals were bronze and have now been lost but the Roman copies have allowed us to understand and perceive what they must have been like in great detail. The one thing they have not allowed us to see is the vivid colours which were often applied to the statues. Traces are sometimes sufficiently visible to allow us to see how bright the colours used might have been.
Having said all this, even in the art of sculpture the Romans eventually impressed their own character which tended towards the description of actual events and compositional structures akin to those of modern publicity: aimed at an appeal for mass audiences. We can see evidence of this growing artistic movement in works starting from the Columns of Trajan and Antoninus right through the following centuries and into the Dark Ages.
For anyone particularly interested, it is worth noting the stylistic difference between the two columns (Trajan and Antonine) which in spite of being separated by “only” eighty years show a marked change in style and execution. This stylistic mutation can also be observed in some of the sculptural relief work which dates to the period of Antoninus but was re-employed in the Arch of Constantine. An interesting example of the change is in representation of the Emperor: the earlier column will show the emperor’s potrait in profile whilst later artistic conventions will portray figures of importance, such as the emperor-god, face on.