program of the Area Martis
Piranesi seems to have designed the Area Martis with the writings of Josephus in mind (as cited in Plattus "Passage into the City"). Piranesi calls the immediate zone around the adjacent Templum Martis "apparatorium triumphatorium"--place of preparation for the triumphal procession, and the many tabernae surrounding the Area Martis seem to be there to accomodate the triumphator and his troops the night before the day of procession. See Plattus p.104-5.
The first arch the procession goes through (and actually the only arch the way goes through within the Ichnographia) is the arch of Trajan. Although there is nothing spectacular in terms of triumph per se that is associated with Trajan. ...the "planned" lineage (literally) going from Trajan to Hadrian to Antoninus Pius along the longest axis (of life) -- from arch to tomb to arch--which corresponds with the historical lineage of imperial sucession. ...all the emperors from Nerva to Antoninus Pius are clearly "marked throughout the Horti Domitiae--there is a statue of Nerva beside the Templ. Plotinae.