A Roman invasion of medieval Europe would face castles and raided supply lines

What would happen if a Roman army invaded medieval Europe?

It would face repeated castle sieges and vulnerable supply lines, although Roman siege skill complicates the prediction that it would simply starve outside the fortifications.

A Roman army invading medieval Europe would encounter a landscape crowded with castles. One panel member imagines the army struggling to feed itself while its opponents wait behind fortifications. Another points out that Roman armies were highly capable at siege warfare, challenging the idea that a castle alone would stop them. The reply shifts to the supply lines: defenders could raid them while the invaders were occupied with repeated sieges. The discussion leaves that disagreement open, making logistics and fortifications the central problems in the counterfactual.