Rome's integration of Isis

In the first millennium BCE, Osiris and Isis became the most widely worshipped Egyptian deities, and Isis absorbed traits from many other goddesses. Rulers in Egypt and its neighbor to the south, Nubia, built temples dedicated primarily to Isis, and her temple at Philae was a religious center for Egyptians and Nubians alike. Her reputed magical power was greater than that of all other gods, and she was said to protect the kingdom from its enemies, govern the skies and the natural world, and have power over fate itself.

In the Hellenistic period (323–30 BCE), when Egypt was ruled and settled by Greeks, Isis was worshipped by Greeks and Egyptians, along with a new god, Serapis. Their worship diffused into the wider Mediterranean world. Isis's Greek devotees ascribed to her traits taken from Greek deities, such as the invention of marriage and the protection of ships at sea, and she retained strong links with Egypt and other Egyptian deities who were popular in the Hellenistic world, such as Osiris and Harpocrates. As Hellenistic culture was absorbed by Rome in the first century BCE, the cult of Isis became a part of Roman religion. Her devotees were a small proportion of the Roman Empire's population but were found all across its territories. Her following developed distinctive festivals such as the Navigium Isidis, as well as initiation ceremonies resembling those of other Greco-Roman mystery cults. Some of her devotees said she encompassed all feminine divine powers in the world.

Authorities in the Republic tried to define which cults were acceptable and which were not, as a way of defining Roman cultural identity amid the cultural changes brought on by Rome's expansion. In Isis's case, shrines and altars to her were set up on the Capitoline Hill, at the heart of the city, by private persons in the early first century BCE. The independence of her cult from the control of Roman authorities made it potentially unsettling to them. In the 50s and 40s BCE, when the crisis of the Roman Republic made many Romans fear that peace among the gods was being disrupted, the Roman Senate destroyed these shrines, although it did not ban Isis from the city outright.

Egyptian cults faced further hostility during the Final War of the Roman Republic (32–30 BCE), when Rome, led by Octavian, the future emperor Augustus, fought Egypt under Cleopatra VII. After Octavian's victory, he banned shrines to Isis and Serapis within the pomerium, the city's innermost, sacred boundary, but allowed them in parts of the city outside the pomerium, thus marking Egyptian deities as non-Roman but acceptable to Rome. Despite being temporarily expelled from Rome during the reign of Tiberius (14–37 CE), the Egyptian cults gradually became an accepted part of the Roman religious landscape. The Flavian emperors in the late first century CE treated Serapis and Isis as patrons of their rule in much the same manner as traditional Roman deities such as Jupiter and Minerva. The cults also expanded into Rome's western provinces, beginning along the Mediterranean coast in early imperial times. At their peak in the late second and early third centuries CE, Isis and Serapis were worshipped in most towns across the western empire, though without much presence in the countryside.[145] Their temples were found from Petra and Palmyra, in the Arabian and Syrian provinces, to Italica in Spain and Londinium in Britain.

My closeup of the Marble statue of Isis found at Hadrian's Villa that I photographed at the Capitoline Museum in 2005.

Marble statue of Isis, the goddess holds a situla and sistrum, ritual implements used in her worship, from 117 until 138 CE, found at Hadrian's Villa (Pantanello), Palazzo Nuovo, Capitoline Museums, courtesy of  Wikimedia Commons contributor Carole Raddato.

Statue of Isis-Persephone holding a sistrum. Temple of the Egyptian gods, Gortyn. Roman period ( 180-190 CE) at the Archaeological Museum in Herakleion, courtesy of Wikimedia Commons contributor Wolfgang Sauber.

Bust of Isis-Sothis-Demeter. White marble, Roman artwork, second part of Hadrian's reign, ca. 131–138 CE. From the gymnasium in the Villa Adriana, near Tivoli, courtesy of Wikimedia Commons contributor Marie-Lan Nguyen.

Roman statue of Isis at Kunsthistorisches Museum in Vienna, Austria courtesy of Wikimedia Commons contributor Manfred Werner. 

Head of divinity, possibly Isis, 2nd century CE, at the Musée Saint-Raymond courtesy of Wikimedia Commons contributor Daniel Martin.

Roman statue of Isis from the 1st - 2nd century CE at the Museo Nazionale Romano, Terme di Diocleziano, courtesy of Wikimedia Commons contributor Szilas.