Lactantius

“ His disease had now become more grievous and oppressing; yet he caused himself to be brought out, in order to dedicate that circus which, at the conclusion of the twentieth year of his reign, he had erected. Immediately he grew so languid and feeble, that prayers for his life were put up to all the gods. ”

“ The fit of stupor, resembling death, happened on the ides of December; and although he in some measure recovered, yet he never attained to perfect health again, for he became disordered in his judgment, being at certain times insane and at others of sound mind. ”

“ The wicked plan having been carried into execution, Diocletian, whom prosperity had now abandoned, set out instantly for Rome, there to celebrate the commencement of the twentieth year of his reign. That solemnity was performed on the twelfth of the kalends of December; [1] and suddenly the emperor, unable to bear the Roman freedom of speech, peevishly and impatiently burst away from the city. ”