The Lord acknowledges Pergamum as being where Satan has his throne. This most plausibly relates to the throne-like altar of Zeus, itself a symbol of the idolatry that held sway in Pergamum. Yet these Christians remained true to the name of Jesus, the only Lord, Saviour and God incarnate.
Beasley-Murray, G. R. (1994). Revelation. In D. A. Carson, R. T. France, J. A. Motyer, & G. J. Wenham (Eds.), New Bible commentary: 21st century edition (4th ed., p. 1429). Inter-Varsity Press.