Revelation 2:13 (ESV)

13 “‘I know where you dwell, where Satan’s throne is. Yet you hold fast my name, and you did not deny my faith even in the days of Antipas my faithful witness, who was killed among you, where Satan dwells.

We know only that he was a faithful witness to the Christian faith in the city, and because of that he was killed. The initial readers of Jesus’ letter to Pergamum undoubtedly remembered well the details surrounding Antipas’ death. (Early writers in church history indicate that he was minister of the Christian church in this city and was required to offer a sacrifice to Caesar; he refused and so was stuffed inside a hollow bronze pig and slowly roasted.) His martyrdom for the gospel gave evidence that Satan indeed had a powerful following in this city.