being Italy is a essentaly fortress with mountains at the top and ocean all around

Enh, it was pretty vulnerable for most the middle ages. Magyars could simply avoid the border forts, the german Kings/Emperors would either control or bribe the castles in the passes and the Med was basically a highway to funnel islamic raiders towards Italy. Hell, they even had permanent presences up to Provence.

https://en.wikipedia.org/wiki/Fraxinetum