The pocket knife is not a modern idea. The earliest known pocket knives date to at least the early iron age. A pocket knife with bone handle was found at Hallstatt, dating to around 600-500BC. They remained rare until modern times compared to knives with fixed blades. For most of history, knives were worn inside sheaths or scabbards attached to the belt. Pockets in clothing is a relatively modern invention. Before this, pockets or pouches were attached to belts, in which these early folding knives would have been carried. In more modern times, it is often illegal to carry fixed blade knives, which has made pocket knives much more common.