Rome served as the epicenter of the Spell of Humility cast by the Roman Magus in C.E. 10.  New Olympus seems to have had some cultural influence from Rome, since it has a Senate-House (and Jove bears the name of a Roman god).  In 1050, Macbeth went on a pilgrimage to Rome, and gave much money there to the poor.  In 1994, Goliath remarked that the roads of Manhattan were "finer than those the Romans built" throughout Rome and Europe during the time of the Roman Empire. Other than this, it is unknown how or when the city, or the former empire, will factor into the series.
- Rome at Wikipedia, the Free Encyclopedia