My frontier garrisons were overwhelmed and destroyed. To make matters worse, the Sassanids immediately invaded me from the east, and their army was 3x larger than my starting forces. I came to the unavoidable conclusion that ERE units simply suck.
Despite re-arranging my troops, the result was exactly the same: my entire army destroyed within a matter of moments, with very low casualties to the enemy (Despite that they were attacking with low-quality units and my men are supposed to be heavy infantry). Horrified, I decided to reload and try the battle again. Basically, they all died almost immediately, while they inflicted negligible damage on the enemy. Despite supposedly being heavy infantry, it was less of a battle and more of a massacre. I was outnumbered 1700 against 2800 men, and my troops were completely useless. But as soon as I ended the first turn, the barbarians attacked me.
My first move was to try to combine my two armies in Europe, hoping they might then have a chance. You have two small, weak armies and not much money. The problem is, the barbarians have two large armies inside your territory on turn 1 (near Thessalonica). I've just started my first campaign as the Eastern Roman Empire… and I am being destroyed! This campaign is really difficult.