August 13 is the feast date of Hippolytus of Rome, martyred in 235 CE while exiled by the Empire to Sardinia. Even as persecutions of Christians went on under Emperors Septimus Severus and Maximinus Thrax, Hippolytus didn't keep a low profile with his coreligionists. He accused the standing pope of embracing the heresy of modalism, and even challenged papal authority by briefly accepting a rivaling bishopric over Rome.
Hippolytus' books included a commentary on Daniel; and his On Christ and Antichrist propounded a 6000-year Earth, detailing events that would lead to the world's demise around 500 CE. (Lactantius later subscribed to the same "hexameron" chronology.)
In his martyrdom, Hippolytus was believed to have been dragged to death by horses, which led, through a bit of reverse logic, to his being named their patron saint.
