Leo the Deacon
The "Athanatoi" were a body of young men of noble status that was originally raised by John I Tzimiskes (r. 969-976) in 970 for his war with the Rus', where they played a decisive role in the battles before Preslav and during the Siege of Dorostolon. The unit was commanded by a "domestikos", as with most of the other "tagmata" (the professional standing regiments), and on campaign camped near the imperial bodyguard, the "Hetaireia". The contemporary historian Leo the Deacon describes the "Athanatoi" as heavily armoured shock cavalry, "sheathed in armour" or as "armed horsemen adorned with gold". Tzimiskes' unit was probably disbanded shortly after his death, since it does not appear again in the sources.