The ancient first century city of Pompeii is divided into nine main regions (Regiones), each containing a mix of residential, commercial, and public buildings that offer insights into the daily life and urban organization of this ancient Roman city. The regions are numbered I to IX, and each encompasses a distinct part of Pompeii, reflecting the diverse activities and structures within the city.

Each region of Pompeii offers a unique glimpse into the multifaceted life of this ancient city. From opulent houses with stunning frescoes and mosaics to bustling commercial spaces and significant public buildings, the regions collectively portray a vivid picture of urban life in Pompeii. The division into regions aids archaeologists and historians in systematically studying the city, understanding its urban layout, and preserving its cultural heritage.

The division of the ancient city of Pompeii into regiones (regions) is a modern archaeological and administrative construct rather than a system used by the ancient Pompeians themselves. This division was introduced by archaeologists to systematically excavate, study, and document the site more efficiently.

Giuseppe Fiorelli, an Italian archaeologist who played a significant role in the excavation of Pompeii during the 19th century, is credited with this systematic division. Fiorelli introduced a more organized approach to the excavation and documentation of Pompeii. He divided the city into nine regions (Regiones), further subdividing these regions into insulae (blocks) and numbered buildings within each insula. This method allowed for a more precise and comprehensive recording of the site's layout and findings.

Regio I
The Regio I is situated in the southern part of the archaeological site of Pompeii. It is one of the largest archaeological regions of ancient Pompeii, encompassing an approximate area of 90,000 square meters. It is bound by Via dell’Abbondanza on the north side, Via Stabiana on the west and Via di Nocera on the east. Notable structures in the Regio I are the House of the Europa Ship, House of Menander, House of the Criptoporticus, House of the Lovers, Garden of the Fugitives, House of the Citharist, excavated in phases during the 19th and 20th centuries CE, and the Fullonica of Stephanus, an industrial laundry that provides insight into urban craft economies. It encompasses a combination of residential and commercial spaces, reflecting the socio-economic diversity of the city's southeastern edge.

Regio I Insula IV
The Regio I Insula IV insula IV of the Regio I is situated in the north-eastern corner of the Regio I. It is adjacent to the Via dell’Abbondanza on the north, Via Stabiana on the west, Vicolo del Menandro to the west and Vicolo el Citarista to the east. The insula covers an area of some 4,200 square meters. It includes the Casa del Citarista (House of the Citharist), covering an area of some 2700 square meters, one of the largest residential complexes in ancinet Pompeii.

Regio II
Located directly east of Regio I, Regio II is also part of the southeastern section of Pompeii. It is primarily characterized by large-elite residential building complexes, entertainment venues interspersed with some smaller residential structures, workshops and commercial spaces, forming a transition zone between the urban core and outlying areas. Early excavations date back to the Bourbon period in the 18th century and were later formalized under Fiorelli’s stratigraphic system. Notable structures in the Regio II include a grand amphitheater, House of the Garden of Hercules, Praedia of Julia Felix, House of Venus in the Shell, House of Octavius Quartio, House of the Floral Lararium,

Regio III
Regio III occupies a the eastern end of the central area of Pompeii, running alongside the eastern stretch of Via dell’Abbondanza. Although it mostly remains unexcavated at the moment, it features some noteworthy structures, including House of the Gladiators (Schola Armaturarum), excavated in the early 20th century. These buildings reflect a focus on residential and military associations, with some evidence of artisan workshops. Excavations carried out in 1913–1915 CE revealed intricate wall paintings and electoral graffiti, indicating the area's involvement in the social and political life of Pompeii.

Regio IV
Regio IV forms a relatively smaller triangular area in the northern end of the archaeological site. It lies north of the Via di Nola, along the eastern stretch. The area remains unexcavated.

Regio V
Regio V lies in the central-northern part of Pompeii and includes several newly excavated structures such as a thermopolium uncovered in 2019, which features vibrant frescoes and in-situ food remnants. The House of the Silver Wedding, excavated in the late 19th century is another important structure in this area, exemplifying high-end residential architecture with a peristyle garden. The Regio V also includes the so-called House of Leda and the Swan. This regio illustrates a blend of elite and commercial spaces and has been the focus of renewed archaeological interest due to ongoing stabilization and excavation efforts under the Great Pompeii Project. Bound by the Via di Vesuvio it also remains unexcavated for the most part.

Regio V Insula I

Regio VI
Regio VI, located northwest of the Forum area, is dominated by elite residences including the House of the Faun, House of the Dioscuri, House of the Surgeon, House of Sallust, House of the Vettii, House of the Tragic Poet and the House of the Prince of Naples, the latter opened ceremonially in 1898. Excavated largely in the 19th century, this regio showcases some of Pompeii's finest examples of Fourth Style wall painting and elite domestic architecture. The region is primarily residential, with a clear emphasis on social display and urban prestige.

Regio VI Insula III

Regio VII
Regio VII, situated in the south-western part of the archaeological site on the western edge of Pompeii near the Porta Marina gate, is the most important and significant area of ancient Roman Pompeii. It not only features residential structures but extensive public infrastructure as well. Key structures include the Roman Forum, House of the Wounded Bear, Stabian Baths, Temple of Fortuna Augusta, Suburban Baths, Forum Baths and the House of the Sailor, which integrates a bakery and storage facilities. Excavations here were intensified in the mid-20th century, with restoration efforts continuing into the present. The proximity to the main entrance and public amenities suggests a socially dynamic area with mixed-use functions. It is bound by the Via dell’Abbondanza on the south side.

Regio VIII
Regio VIII, lying south of the Regio VII and west of the regio I, occupies the south-western corner of the archaeological site. it is one of the most extensively studied and excavated regions of ancient Pompeii. Available data indicates a combination of street-facing shops and upper-story apartments, suggesting a mixed commercial-residential use. It includes, the theater area, one of the two large entertainment venues in ancient Pompeii, along with a Sanctuary to Isis, comittium and administrative halls of the aediles, grand basilica, Sanctuary of Venus and a modern Antiquarium (museum).

Regio VIII Insula IV
The Insula 4 lies at the north-eastern corner of the Regio VIII, and includes a number of notable residential, commercial and industrial structures. It is located adjacent to the Via dell’Abbondanza to the north, Via Stabiana (Strada Stabiana) to the east, Via del Tempio d'Iside to the south, and Via del Teatri to the west. The Stabian baths are located directly to the north across the Via del'Abbondanza. In this part of the archaeological site, the House of the Cornelii is the largest residential complex.

Regio IX
Regio IX is located in the central part of Pompeii, bounded by Via Stabiana (west), Via dell’Abbondanza (south) and Via di Nola (north). It comprises a dense aggregation of elite homes, workshops, retail spaces, and recently discovered private bath complexes. Notable residences include those of Epidius Sabinus, Julius Polybius, Obellius Firmus, and most importantly the House of Thiasus. Excavations began under Karl Weber in the 18th century, continued under Fiorelli in the 1860s, and were resumed in the early 20th century and again in 2023 under the Great Pompeii Project. This regio exemplifies the urban complexity of Pompeii, integrating luxury, commerce, and craftsmanship in a densely built environment.