Begun in 107, was completed in 113 AD by the architect Apollodoro di Damasco. Man, to create a useful space for the construction of the Forum, he cut the seat that formerly joined the Campidoglio and Quirinale. Testimony is its inscription at the base of Trajan's Column: "ad declarandum quantae altitudinis mons et locus tantis operibus sit egestus" (to indicate what was a high hill with these works was demolished). The column thus also served to indicate the original height of the hill cut to free the area for the Forum.

Ugo Ojetti, "Roman boy" class 1871, recalls in his memories that he went down early in the morning from his home in Piazza San Claudio, and for little money bought goat milk. Invariably, at dawn, shepherds and farmers were in town with a small flock in tow, which was announced by the jingle of bells tied around his neck. Goat's milk, lighter and more nutritious than cow's, it was very fashionable and would gorge advertisers to today's snacks: Trajan's Forum was a place too beautiful not to open shop. Not subject to constraints that block the path of the flocks, the area where the work was concentrated by Apollodoro di Damasco (one of the most impressive ancient building which measured 300 meters by 180), gave the scene a pastoral bucolic.

Yet we are far from rural area: a stone's throw from Trajan's column, halfway between the sixteenth century church of Santa Maria di Loreto and that of SS. Name of Mary, the largest ex-votos in the world. Was in fact built "for grace received" after the liberation of Vienna from the Turks in 1683. Of the dense cluster of homes surrounding this oasis of ancient Rome, whose excavation was begun by the French in 1812, would disappear every trace in the Fascist period, when its foundation was founded the way of the Empire. Even the original brick stairway, which breaks the horizontal plane with its vertical commemorative monument the exploits of Trajan, the streetlight and cathedrals, will partially lost.