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 illuftrios who held the first rank among those called honorati; that is, the praefecti praetorii, praefecti urbis, treasurers, comites, &c.

There were, however, different degrees among the illuftrios; as in Spain they have grandees of the first and second class, so in Rome they had their illuftrios, whom they called great, maiiores; and others less, called illuftrios minores.—For instance; the praefectus praetorii was a degree below the master of the offices, though they were both illuftrios.

The Novels of Valentinian distinguish as far as five kinds of illuftrios, among whom, the illuftrios administrares bear the first rank.