In the 899 Kletorologion of Philotheos, the decanus (transcribed into Greek as δεκανός, dekanos) was a mid-level functionary, serving under the protasekretis.
In the late 9th-century hierarchy, however, as related by the Klētorologion of Philotheos, it was one of the lower dignities intended for "bearded men" (i.e. non-eunuchs), ranking between the spatharios and the stratōr.
It was published in September 899 during the reign of Emperor Leo VI the Wise (r. 886–912) by the otherwise unknown prōtospatharios and atriklinēs Philotheos.
The journal was initially based at the Philosophy Faculty in Nikšić (Montenegro), but since 2006 it has been published at the Faculty of Orthodox Theology at the University of Belgrade.
According to the Klētorologion of Philotheos, the holders of the dignity were distinguished between eunuchs (ektomiai) and non-eunuchs (barbatoi, "bearded ones").
Like him, he was a subordinate official of the urban prefect, also known as the Eparch of Constantinople; in Philotheos's Klētorologion of 899, he is indeed shown as being of relatively lowly rank.