Below is a satellite image showing the old quarters of the French city of Lyon, by the river Saone. As you can see, there are a couple of streets running parallel to the river but not many side streets connecting the parallel streets. Using the distance scale given at the bottom of the map, I would guess the connecting streets are located about 200 meters apart, which should be a comfortable two minute walk or less, assuming you are a tourist. But when you are a 15th century silk trader carrying bolts of precious silk weighing hundreds of pounds, the shorter the distance you have to travel the better. So these traders began to take shortcuts cutting through houses and private courtyards to reach the opposite street. Over time, these shortcuts began to develop into a well-known network of passageways called traboules. The word comes from the Latin trans ambulare which mean “to cross”.

Satellite image of Old Lyon.