The sanctuary comprises a sacred precinct (templum) enclosed by walls and includes the main temple, ritual altars, paved courtyards, and several ancillary rooms likely used for initiation rites, priestly functions, and ritual preparation. It reflects the integration of Egyptian religious traditions into Roman cultic life and served as a center of Isiac worship until the city's destruction in 79 CE.

The temple and the structures pertaining to it - which make up a full fledged sanctuary area - was unearthed between 1764 and 1766 CE. Almost intact, it extensively and decisively contributed to making Pompeii known to the world.

The earliest construction of the temple dates to the end of the second century BCE, a time of great economic and cultural affluence for the city; it was thanks to trading with the east, first among which the emporium of Delos , that the cult of the goddess spread to Italy, first to Pozzuoli and later to Pompeii.

The area chosen for the construction - behind the grand or large theater and close to a gate that led to the sea - was already sacred owing to the presence of an ancient temple of Athena. The first temple was completely destroyed in the earthquake of 62 CE. An inscription on the door to the sanctuary provides details that the reconstruction starting from the foundation was entirely financed by Numerius Popidius Ampliatus, a freedman from an ancient Samnite family, who had the temple rebuilt in the name of his six-year old son Celsinus.

The sanctuary was made up of several different buildings, altars, cultic chapels, and gathering areas. The central temple it self was situated in a sort of peristyle surrounded by arcades. Unfolding upong the walls, entirely painted in red, was a ritual procession that portrayed the participation of several priests,each of whom performing a different rite. Inside a niche on the south wall, in axis with the main entrance to the temple proper, a fresco depicted the statueof Harpocrates, and a priest about to begin a rite nearby.

circa 80-79 BCE

The salvific goddess par excellence Isis, according to the myth, gathered and assembled the bones of Osiris, her brother and husband, who had been torn to pieces by Seth, their other brother, and brought him back to life for the time it took them to conceive a sin, Horus. The cult of Isis arrived in the west during the Hellenistic period, worshipped by sailors and merchants as the protector of navigators. A distinguishing feature of her cult is the mystery, probably inspired by the Greek bults of Demetra and Persephone. The cult is reserved for initiates and it consisted of a very structured community that was involved in almost everyday rituals. The Egyptian goddess was lo less popular, however, her ability to free a person from slavery, to restore life, and to guarantee a better one, ensured the dissemination of the cult in all social classed of the Roman society.

circa 80-79 BCE

The first temple of Isis in Pompeii was most likely built in the early first century BCE. Sometime during the mid-late first century BCE (in 54 BCE and 30 BCE), the Roman senate had issued proclamations demanding that the cult of Isis and her temples be demolished. It is reported that there were no volunteers to undertake this process, and that the cult only grew in popularity from this point, so much so that the Temple of Isis was one of the only buildings to be fully rebuilt after the earthquake of 62 CE. The extant structure of the Pompeian temple of Isis, is actually the second structure; the earlier building built during the reign of Augustus (circa 27 BCE- 14 CE) was damaged in the earthquake of 62 CE. At the time of the 79 CE eruption of Vesuvius, the Iseum of Pompeii was the only temple to have been completely re-built; even the Capitolium had not been. Although the Iseum was wedged into a small and narrow space, it received significant foot traffic from theater-goers at the Large Theater, businessmen in the Triangular Forum, and others along the Stabian Gate.

circa 80-79 BCE

Temple
The temple proper was the centerpiece of the larger sanctuary dedicated to Isis. It stands on a high podium and is accessed by a frontal staircase, leading to a deep pronaos and a single-room cella that once housed the cult statue of the goddess. Architecturally Roman yet symbolically Egyptian, the structure reflects the religious syncretism characteristic of the early Imperial period. The temple is oriented within a walled sacred precinct that includes altars, a ritual basin (piscina), and subsidiary rooms, likely used for initiatory or priestly functions. Rebuilt with notable care after the earthquake of 62 CE, its restoration was funded by a freedman, suggesting the popularity of the Isiac cult among non-elite and possibly foreign communities in Pompeii. The prominence of the temple within the sanctuary underscores its function as the ritual and symbolic focus of Isiac worship, with ceremonial activities centered on the veneration of Isis as a protector and guarantor of salvation in this life and the next.

circa 80-79 BCE

Ekklesiasterion
The small temple complex also features a large room - called an Ekklesiasterion - at the back of the sanctuary, which functioned as a gathering area for the members of the cult to participate in rituals. The walls of the Ekklesiasterion illustrated various mythological scenes. The Ekklesiasterion includes scenes of Io's arrival in Egypt and subsequent reception by Isis. This hall itself appears to be the most formal with its role in ritual banquets as well as the reunion of initiates.

Behind the temple, a large rectangular space (ecclesiasterion) was used for the meetings of those being initiated in to the Isiac mysteries. The walls were decorated with great landscapes and three mythological scenes that told the story of Io, who protected the Egyptian population.

circa 80-79 BCE

Sacrarium
Next to the Ekklesiasterion was the sacrarium, which stored the temple's prized objects. The sacrarium is also heavily Egyptian influenced with a mural of snakes guarding a wicker basket adorned with lunar symbols.

Another meeting room was located on the northern side; this was smaller and more richly decorated, known as the sacrarium or sacristy, and there was also a storage space. The sanctuary area was completed by a two level residential complex which could be reached from the sanctuary courtyard. Members of the cult and the faithful who were preparing for their initiation lived there.