In the Roman world, this term designated the individual attached to the bedroom cubiculum of persons, normally, of high political and social rank. Particularly important was the cubicularius of the imperial house, who superintended the emperorâ€™s personal service and all the domestic staff of his cubiculum, constituting in practice the princepsâ€™s most trusted bodyguard. In the late empire, the praepositus sacri cubiculi was at the head of this service. The persons mentioned in the Christian inscriptions ICUR I, 1461; II, 6109; Diehl 226 must have been cubicularii of the imperial court or of some noble family.
The duties of the cubicularius attached to the person of the pope cannot have been much different from those of the imperial cubicularius. We do not know when this service was instituted; only that the ministerium cubiculi pontificalis was held by laymen until the time of Gregory the Great 590â€“604, who replaced them with clerics or monks so that these could profit by contact with the pontiff â€™s private life Greg. Gt., MGH Ep. I, 363. In Ordo Romanus I nn. 23, 33, it is the cubicularii who carry the pontifical ornaments and the chair on which the pope will sit into the sacristy of the stational church. The custodes qui dicuntur cubicularii had a totally different function: they were instituted as we know from the Liber pontificalis Duchesne LP I, 239 by Leo the Great 440â€“461 to be in charge of the apostolic tombs super sepulcra apostolorum. These persons, chosen ex clero romano and comparable to the mansionarii, who looked after and maintained venerated tombs near which they often lived, are frequently attested by epigraphy, partly referring to the cubicularii of the two apostolic basilicas of Ostiense and the Vatican ICUR I, 2043; II, 4852, 4865, 5088, 5179, 5180, 5725; CIL VI, 9315, partly relating to tituli urbani and other, extraurban, martyrial basilicas, to which this service had evidently been extended ICUR VII, 17865, 27470. Two mosaic inscriptions at Grado mention cubicularii whose precise function is hard to establish guards of relics, employees of some noble family or of the civil administration?