I just recently learned about the presence of temples dedicated to Egyptian deities in Roman cities (specifically Pompeii), and I was wondering if this was a "two way street", so to speak. I know that Romans tended to merge similar religious figures together, but I am also aware that there were certain figures who were unique to each respective culture.
Ehhhh....yes and no. Prior to the Roman conquest of Egypt (traditionally dated to the Battle of Actium), the Ptolemies had ruled Egypt, set up by Alexander the Great in 323 BCE, and as Macedonians were culturally Greek and worshiped the Greek pantheon. When Herodotus visited Egypt in c. 450 BCE he wrote down his experiences and compared the Egyptian gods as best he could to the Greek ones. Combination gods like Serapis and Harpokrates also sprang up, and slammed Greek and Egyptian religous practices and iconography together.
When the Romans showed up they took over Egypt and, as was the Roman way, pretty much left the religion alone. As you said in the question, the cult of Isis (among others) spread like wildfire throughout the Roman world, but the opposite isn't as true. The Romans changed a LOT about Egyptian religion's administration and power but the practice was left alone for the most part, having already been changed by the Ptolemies and with religious intervention not really being a huge part of the Roman style.
The Egyptians did set up a cult for the Emperor as a living avatar of Horus, and dressed the falcon-god in Roman Imperial military dress. But the major cult centers of various Egyptian gods like Sobek, Osiris, etc remained fairly similar. My area of expertise is pre-Ptolemaic Egypt so if anyone has more knowledge about Roman Egyptian religious practice, their additions would be greatly appreciated.
