During the Middle Ages, Lyon had a flourishing silk trade. In order to allow the silk merchants to transfer their goods from barges in the river, or to and from their storage areas or shops, they had to walk through the narrow streets of the old Lyon (Vieux Lyon). On its own not a problem except when it rained. Silk does not like rain, so the merchants needed to keep their goods dry (plastic wasn’t invented on those days yet). So they thought up a smart system. Throughout the buildings in the older part of Lyon, they transposed passageways. These passageways, called “Traboules“, became an integral part of the building structure of the houses in the old city. Instead of walking the long streets, and getting wet, you would duck into a traboule and exit several streets further, and then ducking into the next one. Today there are some 215 Traboules spread around the “Vieux Lyon” (Old Lyon) and a total of 500 of them all over Lyon. But the vast majority are private and can not be visited. In the old town, some 40 of them are open to visits, but you need to know where they are, since often they are hidden and they are privately owned, forming part of a building so you need to keep quite.