Roman worship of the Egyptian goddess Isis

Greeks were aware of Egyptian deities, including Isis, at least as early as the Archaic Period (c. 700–480 BCE), and her first known temple in Greece was built during or before the fourth century BCE by Egyptians living in Athens. The conquests of Alexander the Great late in that century created Hellenistic kingdoms around the Mediterranean and Near East, including Ptolemaic Egypt, and put Greek and non-Greek religions in much closer contact. The resulting diffusion of cultures allowed many religious traditions to spread across the Hellenistic world in the last three centuries BCE. 

Isis's cult reached Italy and the Roman sphere of influence at some point in the second century BCE. It was one of many cults that were introduced to Rome as the Roman Republic's territory expanded in the last centuries BCE. 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. Their temples were found from Petra and Palmyra, in the Arabian and Syrian provinces, to Italica in Spain and Londinium in Britain.

Image:  Oracle statue of Isis, Roman, Bronze, 150 CE, that I 

photographed at the Neues Museum in Berlin.