 The single arch was the most common, but many triple arches were also built, of which the Triumphal Arch of Orange ("circa" AD 21) is the earliest surviving example.From the 2nd century AD, many examples of the "arcus quadrifrons" – a square triumphal arch erected over a crossroads, with arched openings on all four sides – were built, especially in North Africa.Arch-building in Rome and Italy diminished after the time of Trajan (AD 98-117) but remained widespread in the provinces during the 2nd and 3rd centuries AD; they were often erected to commemorate imperial visits.