Careless soldiers?

Drenthe has never officially been part of the Roman Empire. Yet we find all kinds of Roman items scattered across the province. Pottery from army camps, for example. But also pieces of horse harnesses of Roman cavalrymen. And ‘fibulae’: pins that served to fasten the Romans’ clothes.  
  
How did those items get there? Maybe they were just lost by careless soldiers. Roman armies crossed the Rhine quite regularly, to fight with Germanic tribes to further expand the Roman Empire. It is therefore not surprising that the people in Drenthe felt threatened: how long will the Romans remain below the Rhine? For how long will we be safe here?