ILLUSTRIOUS, ILLUSTRIS, was heretofore, in the Roman empire, a title of honour peculiar to people of a certain rank. It was first given to the most distinguished among the knights, who had a right to bear the latus clavus: afterwards, those were intitled illustrius who held the first rank, among those called honorati; that is, the præfecti pratorii, præfecti urbis, treasurers, comites, &c.
There were, however, different degrees among the illustres: as in Spain they have grandes of the first and second class, so in Rome they had their illustres, whom they called great, maiores; and others less, called illustres minores.—For instance: the præfectus pratorii was a degree below the master of the offices, though they were both illustres.
The Novels of Valentinian distinguish as far as five kinds of illustres: among whom, the illustres administratores bear the first rank.