A Title with The Roman Legions in the late Imperial Period (4th Century AD), The Decanus meant ''Chief of Ten''. While originally thought by Historians that this was a Junior Officer Position, it was probably held by the Modern equivalent Military Rank of Squad Leader (Sergeant).
The Decanus was tasked with Command over a single tent of (8) Soldiers and (2) Servants. In The later Byzantine Empire (Eastern), The Decanus was a similar Military Rank and Title. The Title would migrate from The Field into Roman Imperial Palaces as a Guard Commander (not an Officer).