Unlike private dwellings or commercial establishments, these structures were meant for collective use, serving as venues for governance, public gatherings, leisure, and religious observance. Many of these buildings were financed by the state, wealthy patrons, or local guilds, reflecting their importance in maintaining civic order and fostering social cohesion.

Ostia Antica, as the principal harbor city of Rome, possessed a well-developed network of civic and public structures that supported its administrative efficiency and social life. The city’s forum, the center of political and judicial activities, was surrounded by key public buildings where official decisions, legal matters, and religious ceremonies took place. The theatre, originally constructed under Augustus and later expanded, served as a major venue for performances, public addresses, and gatherings, demonstrating the Roman emphasis on entertainment and civic engagement. Meanwhile, the Barracks of the Fire Brigade (Caserma dei Vigili) housed the city’s firefighting force, a critical institution in an urban environment where fire posed constant risks.

Bath complexes were among the most significant public structures in Ostia, reflecting both the Roman emphasis on hygiene and the social role of bathing culture. The city contained numerous baths of varying sizes and levels of decoration, including the Forum Baths, the Baths of Neptune, and the Baths of the Seven Sages, each catering to different sections of the population. These establishments functioned as community hubs where citizens could bathe, exercise, and socialize. Public porticoes, such as the Eastern and Western Porticus of Pius IX with Loggias, provided sheltered walkways and meeting spaces, facilitating movement and interaction across the city. Collectively, these structures highlight the organized civic planning of Ostia and its role as a microcosm of Roman urban life, where governance, social interaction, and recreation were deeply interconnected.

circa 350-50 BCE

Forum
The Forum of Ostia (Foro), a public square lies at the centre of the commercial district. It is located where the cardo and decumanus intersect, itplayed a central role in the civic and religious life of the city from the foundation of the castrum (fourth century BCE). It was only at the start of the imperial period that this area took on the shape of a true forum, consisting of a large coentral square with the city's main religious and public building arranged around it. Already in this period, the north side of the Forum was occupied by the Capitolium, dedicated to Jupiter, Juno and Minerva, and the south side by the Temple of Roma and Augustus. The west side was bounded by the basilica, used for the administration of justice, and the east side by the imposing public complex of the Terme del Foro. The square was monumentalized in the Hadrianic period, in around 120 CE, with the renovation of the capitolium and the addition of porticoes on the long sides; the open central space was gradually occupied by honorary statues of magistrates and public figures. The district also hosted other important sanctuaries, among which the Republican Sacred Area of Via della Foce stood out for antiquity and importance, alongside craftworking and commercial establishments (the Molino del Silvano, the Thermopolium of Via di Diana and Caseggiato del Larario), and warehouses (Horrea Epagathiana). Near the Forum there were also multi-story residential buildings (Casa di Diana, Caseggiato dei Dipinti and Caseggiato dei Balconi) with fine painted decorations.

circa 90 BCE

Theatre
The Roman theatre of Ostica Antica (Teatro Romano di Ostia) was built under the reign of emperor Augustus at the end of the first century BCE. It was a majestic and imposing structure big enough to hold 2500 people. At the end of the second century it was further amplified to bring it to a seating capacity of 4000.

The theatre was built on the north side of the Decumanus Maximus. The masonry of the present theatre has been dated to the late second century CE. In the facade are sixteen shops with back-rooms. They were behind a portico, entered through arches. Brick pilasters with travertine bases were set against the arches. There were also arches on the second and third level, on the highest level with windows. Inside the portico, to the right of the main entrance, is a well with a travertine well-head from the period of Commodus. The shops had simple wall-paintings.

circa 41-54 CE

Baths of the Provinces
The Baths of the Provinces (Terme delle Province) were discovered underneath a road dating to the early second century CE. The actual size of the baths dating back to the time of Claudius (circa 41-54 CE) is not possible to be determined. The only portion still visible is a fine black and whitemosaic presenting panels with depictions of weapons and geometrical motifs enclosed within a meander border. The central area is adorned with a panel containing depictions of dolphins, flanked by the personifications of the provinces of Spain, Sicily, Egypt and Africa, and of the winds, symbolized respectively by women's heads and men's heads. The figurative motifs probably allude to the development of maritime trade between the provinces of the western mediterranean and Rome following the construction of the port of Claudius.

circa 50 CE

Baths of the Envious One
The Baths of the Envious One or the Jealous One (Terme dell'Invidioso), built circa 50 CE (opus reticulatum), were named after a textual mosaic found in an adjacent shop. Major alterations have been dated to the period of Antoninus Pius (opus latericium). The paintings and black-and-white mosaics have been dated to the first half of the third century CE. The latest masonry in the building belongs to the early fifth century CE. Three brick piers were set against the south facade, belonging to arches that spanned the road. Behind the westernmost one are a few strange decorative elements.

circa 80 CE

Barracks of the Fire-brigade and Augusteum
The imposing Barracks of the fire-brigade (Caserma dei Vigili e Augusteum) reflect the importance attached in the city to the Vigiles (fire-brigade), who acted both as the town's police force and as the fire-fighters. The barracks were built in the late first century CE when a permanent fire brigade was established at Ostia. However, the layout visible today dates from the transformations that affected the entire district in the Hadrian's era (first half of the second century CE). Thecomplex, at least two story high, had a porticoed courtyard onto which opened the fire fighters' rooms and the wash basins, at the back was a shrine from the imperial cult, built in monumental form in the early third century CE. THe corner room, a latrine, was embellished with a shrine dedicated to Fortuna.

circa 100 CE

Baths of Neptune
The Baths of Neptune (Terme di Nettuno) rose, with a strict plan on top of the preceding Domitianic bath complex, of which they utilise, with few modifications, the plan and foundations, occupying an entire insula (block), in the course of the impressive renovation of the area promotedby Hadrian (circa 117-138 CE). These baths constitute an example of bath typology, that integrates itself with the surrounding building fabric and urban street network. The older principal entrance, that opened onto Via degli Vigili was flanked by a latrine and led into a vast room with the mosaic of Neptune. The changing rooms were arranged on the sides. To the north, one entered the baths, within which came in succession axially, a frigidarium for the coldest baths, two tepidaria filter rooms not equipped with basins and two calidaria. The west side was occupied by a palaestra that rose on a large cistern, no longer in use in the second century CE. From the Decumanus, everyone had access to the public spaces and facilities, including the latrine, positioned on the extreme right of the palaestra. The heating system was situated along the perimeter of the building, at a lower level. Hot air was piped from here into the air spaces created under the pavement and behind the walls. The water was supplied by the aquaduct and conserved in a cistern. These Baths of Neptune, grandiose in their structure and internal furnishings, were just one of about twenty bath complex whose high number (an increase occurs in the second century CE) are a direct consequence of the relative ease of the provisioning of water (ground water and aquaduct) and of the almost complete absence of private facilities in the houses. The use of the baths made it possible to discharge, in fact, the more basic norms of hygiene, facilitating access to the medical/curative services (massages, gymnastics, games etc) that were practised there andfavouring social relations.

circa 117-138 CE

Baths of the Seven Sages
The Bath of the Saven Sages or the Wisemen (Terme dei Sette Sapienti), probably built during the Hadrianic period (circa 117-138 CE), takes its name from a painting of the "Seven Sages" decorating a room that may originally havebeenused a tavern and was later incorporated into the baths as a changing room. As is evident from the placement of the entrances, the baths were used not only by the residents of the adjacent buildings, but also by those of the surrounding district. The had a circular frigidarium (room for cold baths) with a domed roof, paved with a mosaic with hunting scenes and plant motifs; other fine mosaics decorated the walls of some niches. A second frigidarium preserves a painting of Venus being born from the waters (Anadyomene), dating to the early third century like the other paintings that survive in the adjacent rooms. Finally, in the south part of the complex were the tepidaria and calidaria (warm and hot rooms).

circa 120 CE

Eastern and Western Porticus of Pius IX with Loggias
The eastern and western porticos of Pius IX with loggias (Portico Est e Ovest di Pio IX con Loggias), located in Regio I, Insula V-VI were constructed during the Hadrianic period (circa 120 CE), these porticoes exemplify the architectural design of continuous barrel-vaulted structures in Ostia, linking the direction of the Tiber River to the Capitolium.

These porticoes flanked a central street, providing covered walkways that facilitated pedestrian movement and offered shelter from the elements. The porticoes were characterized by brick piers supporting the ceilings, with external staircases leading to apartments on the upper floors. At the southern end of each portico were spacious areas referred to as loggias, which featured ceilings supported by brick piers. Historical plans indicate that the floors of these loggias were paved with basalt blocks, suggesting they may have been used as stables. Additionally, at some point, two walls were constructed at the southern end of the central street (Cardo), leaving a space of 3.40 meters, possibly to control access or manage traffic flow.

circa 125 CE

Baths of the Carriage Drivers
The baths of the carriage drivers or the charioteers (Terme dei Cisiarii) were built in the first half of the second century CE, these baths probably belonged wo the guild of the Cisiarii (carriage drivers). The northern part was occupied by the frigidarium (room for cold baths) whose original mosaic floor survives, depicting two concentric wall circuits within which are marine scenes and scenes of the life carriage druvers. Two rooms located at the centre of the complex were heated and decorated with figurative mosaics, belonging both to the original phase and to the later periods. The decoration was completed by fine figurative stucco reliefs on the walls and ceilings, found in a fragmentary state. A noria (wooden water wheel), discovered in the sourthern part of thecomplex, served to draw up and distribute the groundwater needed for the baths to function.

circa 125 CE

Baths of the Six Columns
The Baths of the six Columns (Terme delle Sei Colonne) are located on the western stretch of the decumanus and north of the Schola del Traiano. Starting in the first half of the second century CE the building complex underwent several phases of reconstruction and renovations. A bronze vessel containing 35 silver coins was found on the premises (most probably a foundation deposit). Most of the coins are from the republican period, some from the first century CE (197 BCE - 70 CE). The entrance corridor between the shops leads to the courtyard of the bath complex. In the centre of the courtyard are the six columns that give the building its current name. The courtyard replaces the palaestra. To the south-east is the cold bath, frigidarium, to the south-west are the heated rooms. In the north-west part of the building was a waterwheel lifting the ground water. Above the wheel and below room were the water reservoirs. Another reservoir and furnaces were in another room. In the north-west part of the building was a large latrine.

circa 160 CE

Forum Baths
The Baths of the Forum (Terme del Foro), also known as the Baths of Gavius Maximus (Terme di Gavius Maximus) were built in around 160 CE by Marcus Gavius Maximus, the praetorian prefect of Antoninus Pius. These luxurious public baths (the largest in the city of Ostia) underwent significantrenovations in the fourth and fifth centuries CE, including the construction of a monumental entrance on Via della Forica. Through the cestibules, patrons entered the apodyteria (changing rooms) and a large frigidarium (room with basins of cold water) with high cross vaults. The heated rooms faced south to best exploittheirexposure to sunlight; thefirst room, octagonal in shape, was probably a heliocaminus (room for sunbathing); it was followed by a laconicum (room for steam baths) and warm and hot rooms. the building's rich marble decoration belongs to the restorations of the fourth century CE.

circa

Baths of the Marina Gate
The Baths of the Marina Gate (Terme di Porta Marina) stood on the coast of Ostia Antica, outside the city wall, a little south of the Porta Marina. This gate was crossed by the decumanus maximus in the direction of the coast. The baths' ancient name, "thermae maritimae", emphasized the link with the sea. That appellation is found in a sixth century CE document in which restoration work during the reign of the emperor Valens is mentioned. The baths' foundation is to be placed during the Trajanic or Hadrianic periods, when there was lively building activity connected with the enlargement of Ostia's seaport. The complex is not vast (slightly more than 3200 square metres). The zone best organised in spatial terms is the northern, where the large frigidarium is situated. The Terme di Porta Marina constituted a public space, and their construction was promoted by the central authority, as can be seen from the rich and high-quality sculptural decoration and from a gallery of imperial portraits.