Pergamum was a city familiar with hosting the throne of a kingdom. One developed there with Pergamum as its capital after the fall of Lysimachus (one of Alexander's generals) in 281 BCE. Until 133 BCE, Pergamum was the throne of this Attalid Kingdom when it was peacefully deeded to the Romans because its king died heirless. I find that more than an interesting crossing of paths between the Roman and Hellenistic worlds.
Under Roman hegemony, the city continued to prosper, and became noteworthy for two inventions: parchment and Emperor worship. We can be thankful for the first, not so much for the second. The imperial cult had its very first temple dedicated in Pergamum in 29 BCE, and so the city became the trailblazer in the development of emperor worship. In much the same way that the Whore of Babylon is a prophetic image that is indicative of the genesis of idolatry in Babylon, the Throne of Satan is a prophetic attribution which is indicative of the genesis of emperor worship in Pergamum.
John doesn't leave it alone at that, however, he further states that Pergamum is the place where Satan dwells. In speaking an eschatological word to the church which will be without Apostolic voice thereafter, John says Pergamum is not only the birth place of emperor worship, but is as well the very base of operations for Satan on earth. Given that the focus of the Apocalypse is the return of Christ, John's attributions necessarily focus our attentions on that place as significant in relation to Christ's return.
What do you think that might mean in locating the base of operations of the Antichrist, who will be the ultimate emperor demanding the ultimate worship? For me, it means I must look to Pergamum.