The correct answer to this open question is the following.
Although there are no options attached, we can say the following.
The groups of invaders that made the most limited incursions in the Roman Empire were the Franks.
The Franks were one of the Germanic tribes that tried to incursion the Roman Empire territories. As it is said above, the Franks were not a tribe that repeatedly invaded the Roman Empire territory, but indeed had some incursions.
The Franks inhabited the territories of the Lower Rhine and some others lived next to the Ems River. They were known to be fierce warriors and determined people that invaded some other regions as was the case of modern-day Belgium and the North of France.
