the arch in an early 17th century etching

Apparently, only the northern side of the arch was decorated; all the extant visual sources feature it from this same side.
The arch bore the name of Portugal because the building it leant against on the left (eastern) side of the street, Palazzo Fiano, was the dwelling in Rome of the Portuguese ambassador.

About halfway along today's via del Corso (once called via Lata), by the crossing with via della Vite, up to the mid 17th century a large arch of roman age spanned the street, linking the buildings on the opposite sides. Originally it consisted of a single archway, flanked on each side by a pair of columns; between the latter hung a panel with a relief. Above the whole structure ran a cornice carved with a flourish.

It was originally dedicated to Marcus Aurelius. Some suggest that it may have also belonged to an aqueduct's branch, in particular the one that carried the Aqua Virgo from the Pincio Hill towards the Baths of Nero, located in the Campus Martius district. Partly in favour of this hypothesis are two small fountains, in the shape of drinking troughs, that can be seen in 16th and 17th century images featuring the arch still in place: they would have obviously drawn water from the same aqueduct. But others identify the water viaduct with the arch of Claudius, another structure now no longer standing, which once spanned the same street further south.

After all, also the dating of the arch is uncertain: it is generally agreed that it was built in the 2nd century, probably using parts taken from older buildings. In fact, the subject of its reliefs was emperor Hadrian (117-138) and his wife Sabina. For this reason, since the Middle Ages the Arch of Portugal had also been referred to as Arch of Hadrian, but also other names were used, such as Arch of San Lorenzo in Lucina (the main church of the district, located in the nearby square), Arch of Tropholi, referring to the trophies of an obscure victory, or Arch of Tripoli, likely referring to three cities (Greek tri polis) celebrated for some reason, or Tres Faciclas or Facicelas (obscure meaning).

It was taken down by pope Alexander VII, in 1665; a plaque was hung on Palazzo Fiano, remembering the arch on the spot where it stood.

The removal, as well as other refurbishment works during the following years, aimed to improve the traffic along the street. In fact during Carnival, in via del Corso the famous Barbary Horse race was held, for which the arch represented undoubtly a dangerous hindrance. The only part spared was one of the two panels in relief, taken to the Capitoline Museums, where it is on display.		the plaque that remembers the arch

The surviving panel features emperor Hadrian and, in the upper part, the glorification of his wife Sabina (d.136 or 137), carried to the heavens by a winged female genius.

		the panel featuring Hadrian and Sabina; (left) aqua fortis by Luigi Rossini (1835), inspired by older images of the arch