The fall of the roman military power

[P. Lilius Frugius Simius]

Publius Johanne sal.

You are 100% right. Due to the raise of the Sassanid Persian Empire to a Superpower, the IV Century emperors, specially Valentinian, were forced to raise the tax pressure close to the limit of the possibilities of the Empire, which meant they could only afford so many soldiers.

According to the Notitia Dignitatum and other sources, the late Empire was maintaining an army between 300,000 to 600,000 soldiers, between limitanei and comitatenses. But despite de fact the Romans managed to stop the Sassanid Empire, they didn't destroy it as a superpower, and as much as 40% of the whole army was deployed permanently on the East (protecting the biggest grainaries of the East, Egypt and Upper Armenia, where today's Georgia).

Add to this the huge invasions and intestinal battles between candidates to the purple that implied the death of big numbers of veterans (Hadrianopolis, but also Frigidus river between East and usurper Eugenius, the incursions of the Goths in 405-406 that, after the death of Stillicho, implied the loss of about 20,000 Goth and other German tribes and coalitions involving Sarmatians, Alans--and whatnot--effectives in the Western comitatenses who joined Alarico, usurpers in Gaul and Britain, the incursions of the Alans, Vandals and Suevi in 405 until 420 which supposed the loss of vast quantities of tax income in those provinces, and the deaths of Constantine troops against the Visigoths, and frontier tribes in the Rhin, and in the campaigns of Aetius against Attila's Huns, and teh Vandals in Africa, etc...)

If the lands you can get money from don't increase (by predating your neighbors'), your tax income is severely reduced from the loss of large portions of your most fertile lands, or by the destruction of other lands that force you to reduce your taxes so they can recover, and your combat ready population don't grow because you are at the limit of your possibilities, you can only do so much...

The difference between East and West is that the Eastern Empire had pretty secured the pass to their fertile crops by Constantinople, and the West, however, had the huge Rhin-Danube frontier to defend, and the Germanic (Vandals, Suevi, Goths, Alamani, Burgundians, Franks, ...) and Iranian (Alans, Sarmatians, ...) tribes pushed by the Huns with nowhere else to go but into the Empire ... Thus, the same economical and military systems survived in the East when they failed in the West... Once the Arabs and Islam attacked the grainaries of the Eastern Empire at the beginning of the VIII Century, the Eastern Empire dissappeared as well, and became the Byzantine Empire (Kingdom) which was substantially smaller and weaker...

This is what I am learning about the late empire... both from "classical" views as Gibbon's, as from Dr Heathers's book I mentioned before... More to learn, but the picture looks cleaner and sharper now...

best regards