Today, I'm going to discuss a truly fascinating aspect of ancient Egyptian culture, that few people know about. It's one of my absolute favorite facets of Egyptian mythology and religious practice during the Ptolemaic and Roman Periods: Greco-Egyptian cults.
After Alexander the Great conquered and hellenized Egypt, there was a tremendous increase in contact and cultural exchanges between the Greeks, Romans, and Native Egyptians, which spurred the creation of so-called "syncretic cults." "Syncretism" is "the amalgamation or attempted amalgamation of different religions, cultures, or schools of thought." Essentially, the Greeks and the Egyptians put their heads together, and combined different elements of their mythologies and pantheons to create "combo-gods" that both group could worship. In the city of Alexandria in particular, these cults flourished and rose to prominence, blending elements of Hellenistic and native Egyptian deities and increasing cohesion between Egypt's rulers and its indigenous and immigrant populations.
One of the most famous Greco-Egyptian deities worshipped during this era was the god Serapis (Remember the Serapeum? It was named after him!). He was an amalgamation of the Egyptian god Osiris and the Greek god Asclepius, and his cult was first introduced and promoted by Ptolemy I Soter. (This was quite obviously a power play, as Ptolemy needed a way to bring his Egyptian and Greek subjects together following Alexander's death). Serapis was also associated with the Egyptian Apis bull cult. According to Roman historian Cornelius Tacitus, Serapis was the most popular and widely-worshipped god in Roman Egypt. Over the centuries, worship of Serapis spread from Alexandria as far away as Afghanistan and parts of Central Asia.
A syncretic deity I find particularly fascinating is Isis-Aphrodite. She was created through a combination of the Egyptian goddess Isis with the Greek goddess Aphrodite (whom the Romans later called "Venus"). Most people don't realize this, but imagery of the goddess Isis nursing her son Horus has been credited with inspiring later depictions of the Virgin Mary and Jesus Christ. In Egyptian mythology, Isis was the sister-wife of the god Osiris (whose role during the Ptolemaic and Roman Periods was usurped by Serapis). The promotion of Isis's cult was most prominently associated with Alexandria and the Ptolemies. The cult spread to Rome in the 2nd century B.C.E., and reached its height during the 2nd century C.E., spreading as far as the Danube region, Germania, and Britain.