With the development of the Imperium, a huge number of different religions with a shorter or longer traditions found themselves within the borders of the Roman state. As a result, a process of intense religious change began. Romans became more and more interested in attractive Eastern cults over time. These include, among others, Egyptian cults, primarily the goddess of Isis and Serapis.
Interestingly, the cult of these deities spread in Italy even before Rome occupied Egypt. For example, Isis was known in Italy probably as early as the 1st century BCE. The early emperors, Augustus and Tiberius particularly disliked Egyptian cults. Only under the rule of Caligula, there was a change in this religious policy in Rome. A temple dedicated to the goddess Isis (Isis Campensis) was then built on the Field of Mars. Emperor Domitian was also a devotee of this goddess, who decided to rebuild this temple after a fire in 80 CE.
To what did Isis and Serapis owe their popularity? The worship of these deities had a long ancient Egyptian tradition, so they were doctrinally consistent and had a developed ethical system. Their strongest point seems to have been their tradition of belief in an afterlife. It could be experienced by people who followed morals and rituals. Of course, over time, the Romans syncretized new deities and enriched their cult with native traditions. For example, Isis has been identified with various mother goddesses (such as Cybele, Minerva, Venus, Diana, Ceres, Juno, Bellona etc.). So she was the goddess of good, care and protector of people. Serapis was seen as Dionysus or as Helios. Despite the syncretic nature of these deities, the organizational forms of worship have retained many traditional Egyptian features. In the western parts of the Empire, eastern deities were romanized very frequently. In this case, however, it was different. Both in the construction of Rome and other cities, many elements were introduced from Egypt or attempts were made to follow them. The aforementioned emperor Domitian, during the reconstruction of the temple of Isis in the Field of Mars, ordered to bring of sphinxes, obelisks and other elements characteristic of Egyptian architecture from Egypt.
Thus, the cult of Isis in Rome retained many traditional features. The goddess priests were largely professional, with a strict hierarchy between them. They were distinguished by a shaved head and white linen robes. Every morning there was a ceremonial opening of the temple and the presentation of the statue of the deity. At the same time, the statue of the goddess was dressed and brushed. Isis also had its attributes. It was a copper rattle (sistrum) and a golden boat, the feet were decorated with sandals embroidered with palm leaves, a symbol of victory. There were also numerous ceremonies later in the day, and spectacular processions were organized on public holidays. Late in the evening, the goddess was said goodbye, and the temple itself was closed. As in other Eastern cults, the most important event for the follower of Isis was the mystery. Most likely they were a recreation of the death of Osiris and the underground journey of Isis, who was looking for her husband.
Another deity that was readily adopted by the Romans was Serapis. The first temple for Serapis was erected in Alexandria. Initially, it was worshipped primarily by the Greeks living in Egypt, who could thus worship an Egyptian deity on the one hand, and on the other hand, could do so within the tradition of Greek cults (the ritual associated with Serapis was more Greek than Egyptian). He had many features characteristic of Greek gods, such as, for example, divine divination during dreams that could help in healing. Interestingly, Serapis were not very popular at that time. The change came with his connection to Isis, which in turn was extremely popular with both the local population and visitors from other lands. The cult of the god Serapis developed in the Empire a little later than Isis. It is surprising that as he became more and more famous in the Empire, his popularity also grew in Egypt itself. The turning point was to be the reign of Emperor Hadrian. He was already given many nicknames then, incl. Augustus, invictus, magnus, conservator, Iupiter. In 127 CE Serapeum was built in Ostia (ie the temple dedicated to Serapis) and since then the city has become an important centre of worship of this Egyptian god. Hadrian vented his interest in Eastern cults during a trip to Egypt in 130/131 CE, during which Hadrian’s lover Antinous drowned in the Nile. Then he decided to expand the Serapis sanctuary in Alexandria. Perhaps he was also initiated into mysteries. Even after returning to Italy, his interest in this deity did not diminish, because he ordered to build of another Sarapejon in his villa in Tibur. The worship of Serapis also seems to be very fond of less wealthy people. At one point, he even overshadowed the position of Isis’s husband, Osiris. Despite Serapis’ very strong ties with Isis, they should not be treated as one religion. It happened that these deities were worshipped together, but much more often separately.
You can ask yourself who actually were the followers of Egyptian cults? Fortunately, we have enough inscriptions and other sources to try to answer this question. Most often, the inscriptions were dedicated to Serapis and Izyda by people related to the administration and merchants. Initially, it was believed that the followers of the goddess Isis and Serapis were also masses of the poorer population. However, this seems unlikely. This undermines the fact that the cult of Isis was disproportionately greater in Italy and Rome itself than in the provinces. In Italy alone, apart from Rome, 200 inscriptions related to the cult of Isis were discovered, while in all eastern provinces only 150. Moreover, Isis in the provinces was an official state deity. This is evidenced, inter alia, by assigning her the nickname Augusta. So it seems that the Egyptian cults played a significant role only in some centers of the Empire. A characteristic feature of the worship of the goddess Isis by the Romans was the greater proportion of women in it than, for example, in the circle of Greek culture. She was worshiped by them, probably due to the fact that she was the patroness of traditionally female values, i.e. family, fertility, motherhood, etc. Women could not only be worshipers of the goddess, but also priestesses.
The cult of Isis and Serapis never developed a strong doctrine, but it undoubtedly tended to explore the spiritual side and the emotional relationship with the deity. This was typical of most oriental religions. The period of the greatest popularity of the cult of this goddess was the 3rd century CE. At that time, Emperor Caracalla ordered another temple to be built for the goddess, apparently even surpassing that of Domitian’s day. With time, however, Egyptian cults lost their popularity, among others, in favour of another new religion, i.e. Christianity.