under Emperor Decius . 250 Hieromartyr Fabian , Bp. of Rome; martyrdom of Pionius of Smyrna . 257-260 Persecution under Emperor Valerian (253-260). 257 Hieromartyr Stephen , Bp. of Rome, and those martyred with him. 255-256 Three Councils of Carthage. 258 Bp. Cyprian of Carthage martyred. 260 Paul of Samosata begins