For that matter, even when the western economy tanked, the Eastern economy was going strong until Heraklios...and that wasn't his fault, really; having most of your empire conquered does that to you. But even so, the Byzantine Economy WAS the most stable in the Middle Ages/Late antiquity, until around the time of Nikephoros III, IIRC. (Admittedly, that's a little later than my field of study. I'm fond of the Isaurians, if by fond, you mean cursing up a storm at them as I research themLong story short, the economy tanking later on wasn't Constantinus' fault. It mostly occurred after the great Rhine irruptions of the first decade of the fifth century (when Vandali, Burgundii, and the lot were able to sweep through Gallia and Hispania and generally disrupt tax collection and agriculture...and cut off relatively prosperous Britannia from imperial control as well), and was vastly exacerbated by the fall of Byzacena and Africa Proconsularis to the Vandali in the 430s and 440s. North Africa was the richest area of the Roman Empire in virtually every period of its existence (save perhaps Egypt in the earlier phases), and losing it was a body blow. And collapse came very quickly once the 468 Carthago expedition failed, making it clear that those revenues would never be recovered...)
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