How long did the Byzantines continue to use the Roman Legionairy system in their military?

I think it still existed in Justinian's time but by the Middle Ages they were relying more and more on Armenian, German and Turk mercenaries.

"Who are the rulers of the lands beyond Guraiz and Burzil? The Darada Rajas."
The Rajatarangini

Thanks Lakedaimon,

So the Eastern Empire relied on heavy cavalry from the start? Interesting. They would have needed it against the Parthians and Sassanians.

Also another question, in their early wars with the Sassanians were Western Legionary units also used in Mesopotamia and Syria or was it exclusively fought by the Eastern Army?

"Who are the rulers of the lands beyond Guraiz and Burzil? The Darada Rajas."
The Rajatarangini

the classic legionary organization changed yet in IV century AD and mainly in the east combined infantry and cavalry units







but also during the first byzantine most of the eastern army was mainly infantry, the easternized byzantines appeared only after Emperor Heraclius reign



during the Roman Empire when main military efforts were needed in the east the bulk and core of the armies was rised from the west using veterans from the Rhine and Danube and Frank and Gothic auxiliaries



the eastern legions were traditionally considered less warlike and disciplined during the Roman Empire





During III century most of the germans serving under Rome were franks and during IV century they were mainly goths



of course Iranian auxiliaries (cataphracts) were used on the Rhine too by Romans

The Cataphracts were mostly Sarmatians and Alans. Thus they were Iranic peoples (much like Pashtuns and Kurds are Iranic) but they certainly werent Iranian as most were from what is today Ukraine, far far away from Persia.

"Who are the rulers of the lands beyond Guraiz and Burzil? The Darada Rajas."
The Rajatarangini

@Darada-Raja

you are correct considering most of the cataphracts in roman service were from Alans and other Sarmatian nations

you can easily remember the 5,000 alan cavalrymen which served Rome in Britain and were at the origin of the legend of King Arthur (have you seen the recent movie ?)

(BTW the european name Alan is from the ethnic "alan")

but the first units of cataphracts in roman service were armenians and partian/persians

those iranian units were very small in number but served for long the Roman Empire mostly on the Rhine border side by side with the Mauretanian light cavalry (and far away from the persian border)

when an important roman (as the infamous Titus Labienus)or a partian/persian (as the Puseus family which descended from a persian officer who flied in the roman camp under Justinian reign and whose descendants were an important roman senatorial family in the late empire)had some "problems" of political nature sometimes he chosed to fly in the enemy empire as a refugee (and serving in his army)