Monti Trevi Colonna Campo Marzio Ponte Parione Regola Sant’Eustachio Pigna Campitelli Sant’Angelo Ripa Trastevere Borgo Esquilino Ludovisi Sallustiano Castro Pretorio Celio Testaccio Prati San Saba

The Roman Regiones
The first urban subdivision was established in the 6th century BC. by Servio Tullio.
4 regions were established within the pomerium:

1. Suburana (Celio)
2. Esquilina (Esquilino)
3. Collina (Quirinale e Viminale)
4. Palatina (Palatino e Velia)

The Capitol was not included in the subdivision, probably due to its character as a defensive citadel and common religious pole, nor the Aventine, still outside the pomerio.
Subsequently in the imperial age, under Augustus there was a new subdivision, which included the city territory which expanded even beyond the borders of the old republican walls. There were 14 regions, all on the left bank of the Tiber except for Transtiberim (today’s Trastevere). They were:

1. Porta Capena
2. Caelimontium
3. Isis et Serapis
4. Templum Pacis
5. Esquiliae
6. Alta Semita
7. Via Lata
8. Forum Romanum
9. Circus Flaminius
10. Palatium
11. Circus Maximus
12. Piscina Publica
13. Aventinus
14. Transtiberim

With the fall of the Western Roman Empire and the decline of Rome as a cultural center, the population decreased and the internal administrative division of the city was also lost. Around the twelfth century, a new subdivision into 12 parts began to emerge, not by imposing it from above but simply for common use. Although the areas were different from the ancient ones, the same term continued to be used: regio in Latin and rione in vulgar.

The districts from the Middle Ages

The boundaries of the districts became definitive and official in the thirteenth century: their number had risen to 13, with the addition of Trastevere. In this period the boundaries were not very clear: the houses were often concentrated in the center of a certain district and the border areas were practically deserted, so it was not even necessary that the borders were delineated with precision.
With the Renaissance began an intense work of arrangement and reorganization of the city. Many parts within the walls that were practically deserted were then urbanized and new roads and fountains were built: it became necessary to clearly delimit the boundaries of the districts.

In 1586 Sixtus V added a fourteenth district in the area of San Pietro: Borgo, creating a situation of equilibrium which, also thanks to the limited population growth, remained such until the 19th century.
In 1798, during the French occupation of the city, a rationalization of the traditional division was attempted, with the establishment of 12 wards (in brackets there is modern correspondence):

1. Terme (parte di Monti);
2. Suburra (parte di Monti);
3. Quirinale (Trevi);
4. Pincio (Colonna);
5. Marte (Campo Marzio);
6. Bruto (Ponte);
7. Pompeo (Regola e Parione);
8. Flaminio (Sant’Eustachio);
9. Pantheon (Pigna e Sant’Angelo);
10. Campidoglio (Campitelli e Ripa);
11. Gianicolo (Trastevere);
12. Vaticano (Borgo);
Dopo poco la Roma napoleonica viene suddivisa nuovamente in 8 parti, ora chiamate ufficialmente Giustizie:
1. Monti;
2. Trevi;
3. Colonna e Campo Marzio;
4. Ponte e Borgo;
5. Parione e Regola;
6. Sant’Eustachio e Pigna;
7. Campitelli, Sant’Angelo e Ripa;
8. Trastevere.

In this way the smaller districts were merged with the larger ones. The merit of this rearrangement was that the French imposed to write their respective names with the area they belonged on all the roads: for the first time there was no ambiguity regarding the borders.
The following period was of relative stagnation without significant changes in the organization of the city.

The districts after the unification of Italy

Everything changed when Rome became the capital of Italy. The continuous influx of immigrants from the rest of Italy plus the birth of all the centers necessary for a capital involved intense urbanization and population growth, both inside and outside the Aurelian walls.
In 1874 the districts became 15 with the addition of the Esquiline, obtained from Monti. At the beginning of the twentieth century, subdivisions of existing neighborhoods began to be seen and the first neighborhoods outside the walls were born.

translation by the author: Alessio Damato