What makes the huns a formidable force for the roman empire?

The Huns were a formidable force to fight. They were able to eat most food without problem which removes the needs for supply trains and such and encourages pillaging. Another reason is that their a cavalry based army which completely decimated roman military since the roman empire consist of flat land and they could outflank, outrun, and could whittle down an army with ease. They also are nomads which means you don't know where they're living and so you can't be on the attack which also gave an advantage. This points that the Huns are a force to be reckon with.