Did secret societies exist when John wrote Revelation, and could they relate to the "synagogue of Satan"?

In Revelation 2:9 and 3:9, John refers to the “synagogue of Satan” — people who claim to be Jews but are not. Some interpreters read this literally (as false converts or hostile groups), while others see it symbolically. My question is: - At the time John wrote Revelation (late 1st century), were there any secret societies, cults, or hidden religious groups in the Greco-Roman world that might have influenced this imagery?