SPOILER ALERT

I was going to make you all wait but considering the intense anxiety such a burning question will raise (and because I don't want the whole school at the next talk) I thought I would give you the short version now.

Triumphal Arches

The consul, or imperator, at the head of a successful army could be awarded an ovation or a triumph by the senate (or he could get nothing). An ovation was a triumph without the spoils or the troops following the Triumphator. But the triumph was the big deal. The biggest of big was when the Triumphator could claim the spolia optima or when he had killed the leader of the enemy forces himself. This only happened three times. Anyway, the Triumphal procession followed a specific route through the city and there are lots of funny stories about generals having to postpone their Triumph because they had attached their chariot to captured elephants who were too big for the streets and stuff like that. Really it was an excuse to parade the power of Roman arms before the Roman people.

The parade was led by the Triumphator in a quadriga (chariot pulled by four horses). His face was painted red because he was the incarnation of Jupiter for a day. The prisoners and all the booty (spolia) would follow the Triumphator and then all the troops would parade past. The celebration could last for days (depending on how much booty the army had won) and resulted in large sections of the city burning to the ground on more than one occasion (troops often got a special bonus in cash from the Triumphator and they sometimes spent it on liquor).

At first I thought the arch was removed from the wall as a concession to the religious requirements of the pomerium but I couldn't think of any specific violation. The general could not enter the city before the triumph and his troops couldn't enter the city at all except in a triumph and then only without weapons. So the dictates imposed by the pomerium were already met.

Then I thought it might have something to do with Janus (the two-faced deity). He is the most Roman of all gods - for reasons I hope the thesis as a whole will make clear. And he did have his own arch but it was paid for by merchants who used the Tiber for shipping. And he has nothing to do with triumphs.

The ancient world was governed by two opposite principles - the ius belli and the ius hosti, the law of belligerents and the law of hosts. Either someone was an enemy and you had no obligations toward them at all or they were kin and you treated them as such. That's how the answer involves old Hostis Hostilius - his name means Friend Foe. The distinction between the two seems cut and dried but it isn't. At least, not in Rome. The frequent elision of the two is part of the logic of empire. And this is why you need to think of the arch in space in order to understand it.

The entire Triumphal route would be thronged with people. The Triumphator would often use manubial funds (money gained by conquest) to pay for temporary seating to allow more people to see the parade. Imagine the streets turned into a tremendous linear stadium, a processional passing through Rome and back again. The riotous citizens are all kin, cheering themselves mad for the glory of the army. The Arch doesn't represent a section of the Roman wall, it is a symbolic gate of the conquered cities. The army doesn't fight its way through, it just marches through to the cheers of adoring fans. The Triumph turns the two ancient laws into the same principle during the procession - it is conquest by force and by absorption. Rome conquers enemies and consumes friends. The arch is the moment and location when these antithetical principles are united to form empire.

See? I told you it was interesting!