Porticus Polae (Portico Pola) «Dione. nel lib. 55.» see chapter 5, article 11.
The west side of the campus [Agrippae] was occupied by the porticus Vipsania or Polae, named from the sister of Agrippa, by whom it had been commenced. It was finished and opened by Augustus. This porticus extended along the via Lata from the aqua Virgo north, -- that is, from the north end of the Saepta, of which it formed a practical continuation, although on the opposite side of the street. It also resembled the Saepta closely in size and construction. In it was a map of the world prepared by order of Agrippa. The porticus appears to have undergone changes in later times, as part of the remains date from the Flavian emperors, and in the second century the intercolumnar spaces were closed up with brick-faced walls, thus making rows of separate chambers. The edifice existed in the fourth century, when it is mentioned by the corrupted name of porticus Gypsiani. At various points in the area covered by the porticus remains have been found of semicircular arches with travertine pillars and pilasters with Doric capitals, and of a travertine pavement and cipollino columns with Corinthian capitals.
The Porticus Vipsania, like the Porticus Alexandri Severi and the Naumachia Domitiani, is one of the buildings along the Ichnographia's Equiria that represents an actual ancient Roman building, however Piranesi situates the Porticus Vipsania further north than its true historical location. The real Porticus Vipsania was within the Campus Agrippae along the Via Lati, close to the Pantheon, and not within the northern region beyond the Aurelian Wall as Piranesi shows it. For modern archeologists, the Porticus Vipsania is interchangeable with the Porticus Polae, and, adding further to the confusion, Piranesi delineates a separate Porticus Polae directly in front of the Pantheon. Needless to say, the inaccuracy of Piranesi's portrayal of the Porticus Vipsania is just one example of why the Ichnographia was never taken seriously as an valid archeological reconstruction.