Decanus

Decanus means "chief of ten" in Late Latin. The term originated in the Roman army and became used thereafter for subaltern officials in the Byzantine Empire, as well as for various positions in the Church, whence derives the English title "dean".

History and functions
The decanus was originally the leader of a contubernium, the squad of eight (8) legionaries that lived in the same tent and the two support units/servants of the contubernium. It must not be confused with the decurio, which was a title given to civic officials and to leaders of 30-strong squadrons (turmae) of cavalry. In Greek texts, it is equivalent to the rank of dekarchos ("commander of ten"). From the 4th century, it became used for palace messengers, particularly those in the service of the Roman empress. They also apparently served as guards at gates, and in the 6th century, John Lydus equates them with the ancient lictors. In the 899 Kletorologion of Philotheos, the decanus (transcribed into Greek as δεκανός, dekanos) was a mid-level functionary, serving under the protasekretis. According to the mid-10th century De Ceremoniis of Emperor Constantine VII Porphyrogennetos (r. 913–959), he was "in charge of the imperial papers" when the Byzantine emperor was on campaign. Sigillographic evidence for the Byzantine dekanoi is relatively rare, although some are depicted in illuminated manuscripts, where their appearance varies considerably, in accord with their varying and changing functions.

In the Church, the term was used in monasteries for heads of groups of ten (10) other monks, for low-ranking subaltern officials of the Patriarchate of Constantinople, and for the ecclesiastic fossores ("grave-diggers").