he oldest arches date back to the second century BC. In total there are more than 100 arches in Italy, 36 in Gaul and 118 in North Africa.
The triumphal arch has a religious origin. After a battle soldiers had to pass through a sacred gate - the fornix - which had to deliver them from the destructive forces that held them their grasp during the military campaigns. Later this ritual was linked up to just one man.
The arch became the symbol of the victory of only one man, the emperor, over the rest of humankind. This personal veneration became more and more common in the course of time.
Triumphal processions passed through the triumphal gates. The wish to hold on to that glorious moment as long as possible was also politically of major concern. It didn't take much time before the 'fornices' lost their temporary character. Instead of wood stone or marble started to be used. That's how they became real monuments.
The gates usually consisted of one to three arched passages, surrounded by columns and reliefs. Often there were statues on top, but unfortunately most of them haven't been preserved.
Some triumphal arches were built in a very special way, with two carriageways intersecting in right-angles. An example of this is the Arch of Janus at the Forum Boarium.