The origins of Rome lie in its situation where two ancient trading routes cross. One is the Via Salaria which runs from the mouth of the Tibur to the Apennines and is the route by which salt was traded. The other route crosses the Tibur at Tibur Island and connects the Etruscan territories with those of the Latins and peoples further south. The site of Rome was a marshy area, prone to flooding in the winter when the Tibur was swollen with rain, especially at the low-lying sites of the future Campus Martius, Forum and Circus Maximus.
From March on the area would begin to dry and provide valuable grazing for nearby communities, especially useful in summer when higher ground would parch in the heat. However, because it was not suitable for arable crops it would probably not have be the particular territory of any tribe or clan. By late summer or early autumn then, it would be an ideal site for a seasonal market and temporary encampment of traders.
How would such a market have been organised in ancient times? The first requirement would have been a means of keeping the peace so that different peoples would feel confident that they could meet in safety and so that disputes could be resolved. It seems likely this would have been done by declaring a market truce. All wars, feuds and disputes would be in abeyance while the market lasted. This would be similar to the Greek Olympic Truce which was promulgated during the games. In historical times the Olympic Truce extended to all the territories of the Greek City States, but it is likely that, at first, it applied only to the site of the festival.
Traders attending the market would be required to swear by the Gods to up hold the truce and thus any breach of it would be not merely a crime but an impiety, punishable by the Gods. Those responsible for upholding the truce and dealing with any breaches or disputes would be acting with religious authority. This helps explain why the Roman magistrates were considered to be fulfilling a sacred role and their persons were held inviolate.
Grounding the origins of Roman institutions in the sacred truce of the market will also explain other peculiarities of Roman custom. If special laws apply to the market it will be important to know how far those law can extend and indeed the Romans had the concept of the pomerium, the sacred boundary of Rome. This was set neither at the walls of Rome nor the limits of the built up area, being older than either of them, but was marked by cippi or boundary stones. Armed troops were not allowed inside the pomerium. Generals had to lay down their commands before entering and soldiers had to change out of uniform and into their togas. In order to make a declaration of war it was necessary to exit the pomerium and conduct a ceremony at the Temple of Bellona just outside of it.
The market place truce needed to be bounded in time as well as space, however. As the market became more necessary to the life of the communities round about, it seems to have extended it existence back from high summer into the spring and people began living permanently on the site. But this would cause other problems, if rogues and criminals were able to use the market truce to allow them to operate with impunity. The Roman calendar however is divided into dies fasti, days on which it was lawful to do business and when the magistrates were active, and dies nefasti, which were frequently days on which festivals were held and when no official business was done and the magistrates did not sit. Did these at one time represent days on which the market truce was not in force and the ordinary customs of the time could be reverted to – perhaps even allowing a bit of extra-judicial vigilantism on the neighbours if it was felt they deserved it?
Obviously, over time, as Rome became ever more a permanent and settled community, and the magistrates took on responsibility for dealing with all kinds of criminal and anti-social behaviour, this would not be such an issue. However, the Romans continued to assiduously note and announce their dies fasti and nefasti. And was a memory of this aspect of the developing Rome one reason it was said to have been founded by thieves and murderers?