Pomerium was a sacred strip of land located both outsides and inside the city walls. As mentioned before this strip of a land had sacred character and marked Rome’s borders. The name post murus means “outside the wall”.
The tradition of marking pomerium was taken from the Etruscans. According to the legend, Romulus in 753 BCE made a furrow with the plough on the west top of Palatine Hill. In this way, he marked the borders of (Roma quadrata). Pomerium was also considered an inner city area. A line of pomerium was sacrificed for underground deities. The border crossing was forbidden and punished by death because of sacrilege. During the marking of the border, a plough was lifted several times to leave some unploughed ground. In these places, city gates were built. The line of pomerium was later marked by stone poles and along this line Romans tried to erect defensive walls. Except for the defensive role, these walls had a big religious importance because they separated chaotic area fulfilled with demons from the inner well-organised one, which possessed its centre. A hole dug at the beginning of each building was considered this centre.
As far as the territory of Rome was being expanded new pomerium was officially marked. Because the whole procedure was done with delay, it created some perturbations within the city. Finally, at the turn of the first and second centuries BCE pomerium included inhabited areas during the reign of Servius Tullius (first half of the fourth century BCE), except Aventine Hill, which was added to pomerium during the time of Emperor Claudius. Pomerium was marked along the defensive walls for the last time during the reign of Emperor Aurelian in 271 CE. Aurelian’s Wall was 19 km long (most parts of it survived to our times).
Pomerium had religious and legal significance. Separate official divinations were made for areas inside and outside pomerium. Staying in the army or execution of death sentences were forbidden within pomerium. Only well-deserved Romans and servants of goddess Westa could be buried there. After the final victory of Christianity over old beliefs in the fourth century CE, the churchyard cemeteries inside the city walls were founded. Pomerium separated civil and military authority. Military orders weren’t in force within its borders. That’s why during uncertain times of the Roman republic military commanders convened the Senat in temples on the Field of Mars, where pomerium didn’t reach. No one armed could enter the city except military triumphs. For this reason on the Field of Mars public meetings took place. As a sign of the unlimited authority of Roman politicians outside the city walls, lictors put their axes in bundles of rods (fasces) whenever they crossed pomerium. No hostes populi Romani (“enemies of Rome”) were allowed to cross pomerium. That’s why envoys were accepted only in the temple of goddess Bellona on the Field of Mars, if they came from hostile lands or lands in a state of truce with Rome. Even Gaius Julius Caesar had to respect pomerium and Cleopatra didn’t dare to cross the city borders during her visit.