Bay leaves originally came from the Mediterranean, in and around Turkey. They're members of the laurel family, the leaves used to make wreaths for Olympic champions in the days before gold medals.
In the Middle Ages bay leaves were popular insecticides and medicine, their lauric acid a good fix for keeping moths and 'feisty humors' at bay. Their rich, gentle, savory flavours paired easily with popular roast meats and the stocks and sauces rapidly developing in Medieval and Renaissance kitchens.
Bay leaves are occasionally available fresh and can be frozen for later use. However, they are mainly sold dried and have a long shelf life.