Functioning as centers of worship, civic identity, and community gatherings, these buildings reflect the religious plurality of Ostia’s population, which included Romans, freedmen, merchants, and immigrants engaged in the city's commercial and maritime activities.

Ostia Antica’s religious landscape evolved alongside its growth as Rome’s primary port, mirroring broader shifts in Roman religion from the Republic through Late Antiquity. In the city’s early phases, temples dedicated to state deities dominated the urban center, particularly around the Forum. During the Imperial period, the influence of Eastern and mystery religions became more pronounced, with the proliferation of mithraea and sanctuaries dedicated to Isis and Serapis. The presence of the synagogue, established as early as the 1st century CE, attests to the existence of a Jewish community within Ostia. Today, these structures survive as archaeological remains, providing insight into the interplay of official state religion, private devotion, and the diverse spiritual practices that coexisted in one of Rome’s most cosmopolitan cities.

circa 120 CE

Capitolium
The main temple of Ostia (tempio della Triade Capitolina), dedicated to the Capitoline triade (Jupiter, Juno, Minerva) was built on the north side of the Forum during the Hadrianic period, in around 120 CE. It stands abouve an earlier cult building dating to the first century BCE, probably dedicated to the same gods and located where the cardo intersect the decumanus. The first century BCE temple was in turn built on top of an older public building, remains of which can be seen in a test pit in the forum square. The Hadrianic Capitolium visible today, erected on a high podium, was built entirely of brick and faced in marble (no longer survives). The cella,preceded by a porch with six columns along the front and two at the sides, has a monumental marble theshold at the entrance; inside, the statues of the three gods originally stood on the podium set against the back wall.

circa 275 CE

Mithraeum of the Delighted
The cult-place of Mithraeum of the Delighted or the Happy One (Mitreo di Felicissimo), dedicated to the eastern god Mithras was installed in an earlier building of uncertain function in the second half of the third century CE. Originally equipped with two podia (benches) and an altar (no longer survives), it has a mosaic floor depicting a krater (vessel) and an altar with a flame, alluding to the use of water and fire in the rituals. Above these are twoPhrygian caps, recognizable from their characteristic shape. Themosaic in the corridor is divided into seven compartments referring to the seven degrees ofinitiation into the cult and seven planets connected to them with their specific ritual objects. In the eighth compartment is an inscription naming the worshipper (Felicissimus) who built the mithraeum, which must originally have been similar in appearance to the other mithraea in Ostia.

circa 270 CE

Mithraeum of Snakes
The Mithraeum of Snakes (Mitreo di Serpenti), was a cult space dedicated to the eastern god Mithras. It was installed in the second half of the third century CE inside an earlier complex with shops. One of the back rooms of a shop was transformed into a cult space where the podia (side benches) and a small altar were madefrom the reused building materials. The mithraeum retained the painted decorations of the preceding phase (circa second century CE), probably belonging to a lararium (shrine of the household gods), depictingtwo snakes, a male identified by a crest anda female, on either side of a Genius with a veiled head anda cornucopia inhishandto symbolize abundance. Since they were connected to the earth, snakesalsoplayed an important role inMithraic religion.

circa

Temple of Ceres or the Divinized Emperors
The temple of godess Ceres (Tempio di Cerere), also known as the temple of the divine emperors (degli Imperatori Divinizzati), situated in the center of the Piazzale delle Corporazioni, adjacent to the theater, this brick temple dates to the reign of Emperor Domitian (circa 81-96 CE). Scholars suggest that Domitian himself may have commissioned the temple to honor the cult of deified emperors. Notably, an arm of a colossal statue, possibly representing Domitian, was discovered in the southwestern part of the square, reinforcing the temple's imperial association.

circa

Serapeum
The Temple of Serapis (tempio dei Serapei) was linked to the House of the Serapeum (Casa dei Serapei) to the south and the House of Bacchus and Ariadne to the north by passages and a corridor behind the buildings. Serapis, an Egyptian deity, resulted from the syncretism between Osiris-Apis (hence the name Serapis) and Jupiter. Brick stamps indicate that the building was constructed between 123 and 126 CE. It is likely mentioned in the Fasti Ostienses, the official calendar of the city, and if so, it was donated by a private individual named Caltilius P... and inaugurated on January 24, 127 CE, the birthday of Emperor Hadrian.

The temple complex was constructed using opus mixtum. The facade featured a central porch, possibly dating to the end of the second century CE. The bases of two columns and two marble-lined niches have been preserved. In the porch is a black-and-white mosaic depicting the bull Apis (a relief of Apis was found nearby). The porch likely once bore a triangular inscription, which was later broken in two and reused as pavement in the building.

circa

Sanctuary of Attis
(Santuario di Attis)

circa 50 CE

Synagogue
The synagogue of Ostia Antica, built for the local Jewish community in circa mid first century CE is possibly one of the oldest in the Western Mediterranean. The current structure, completely reconstructed in the fourth century CE, was accessible through a vestibule, that led in to the area reserved for religious functions and prayer. The cult hall had a colonnaded entrance and at the back was the bimah (a raised platform for reading the texts of the Torah), facing towards Jerusalem. On the entrance side of the hall was the apsidal shrine (illustration) hosting the scrolls of Torah, surmounted by corbels and decorated with theimage of seven armed candelabrum (menorah). The large adjacent hall, with benches along the walls, may have been used for meetings or for teaching, whilst another room with an oven and a counter served for the preparation of unleavened bread.

circa

Sanctuary of the Augusti
The so called sanctuary of the divinity of the Augusti (Sacello dei Lares Augusti), a circular monument, stands at the centre of the Forum square and is traditionally interpreted as the "Shrine of the Lares Augusti" (the gods who protected the emperor). The identification is based on the attribution to this monument of an inscription, not found in sity, commemorating the construct of a temple dedicated to thiscult around the mid first century CE. Another theory identifies the monument as a nymphaeum, in part based on the presence of an internal coating of hydraulic lime.