ILLUSTRIOUS, ILLUSTRIS, in the Roman empire, a title of honour peculiar to people of a certain rank. It was first given to the most distinguished amongst the knights, who had a right to bear the latus clavus; but afterwards those only were entitled illustrious who held the first rank amongst the persons called honorati, that is, the praefecti pratorum, praefecti urbis, treasurers, comites, and others. The Novels of Valentinian distinguish as many as five kinds of illustres, amongst whom the illustres administratores bear the first rank.