A complex of five grandly conceived complexes flanked with colonnades, the Fori Imperiali contain monuments of triumph, law courts, and temples. The complexes were tacked on to the Roman Forum, from the time of Julius Caesar in the 1st century BC until Trajan in the very early 2nd century AD, to accomodate the ever-growing need for buildings of administration and grand monuments.
From Piazza del Colosseo, head northwest on Via dei Fori Imperiali toward Piazza Venezia. Now that the road has been closed to private traffic, it's more pleasant for pedestrians (it's closed to all traffic on Sunday). On the walls to your left, maps in marble and bronze, put up by Benito Mussolini, show the extent of the Roman Republic and Empire (at the time of writing, these were partially obstructed by work on Rome's new subway line, Metro C). The dictator's own dreams of empire led him to construct this avenue, cutting brutally through the Fori Imperiali, and the medieval and Renaissance buildings
that had grown upon the ruins, so that he would have a suitable venue for parades celebrating his expected military triumphs. Among the Fori Imperiali along the avenue, you can see the Foro di Cesare (Forum of Caesar) and the Foro di Augusto (Forum of Augustus). The grandest was the Foro di Traiano (Forum of Trajan), with its huge semicircular Mercati di Traiano and the Colonna Traiana (Trajan's Column). You can walk through part of Trajan's Markets on the Via Alessandrina and visit the Museo dei Fori Imperiali, which presents the Imperial Forums and shows how they would have been used through ancient fragments, artifacts, and modern multimedia.