Institutio Oratoria
Quintilian
Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.
And yet at a slightly earlier date iussi which we write with a double s was spelt with only one. Further optimnus maximus, which older writers spelt with a u, appear for the first time with an i (such at any rate is the tradition) in an inscription of Gaius Caesar. [*](Caligula, the first of the Caesars to adopt this title.)