Complex sentence: Hermagoras and Fortunatus may have been martyrs of Singidunum (Belgrade) who were killed there around 304 during the religious persecutions led by Emperor Diocletian.
Split into simpler sentences: Hermagoras and Fortunatus may have been martyrs of Singidunum (Belgrade) who were killed. There around 304 during the religious persecutions led by Emperor Diocletian.