The geology of the Ohio River, with but a single series of rapids halfway in its length from the confluence of the Monongahela and Allegheny rivers to its union with the Mississippi, made it inevitable that a town would grow on the site. Louisville, Kentucky was chartered in the late 18th century. From its early days on the frontier, it quickly grew to be a major trading and distribution center in the mid 19th century, important industrial city in the early 20th, declined in the mid 20th century, before revitalizing in the late 20th century as a culturally-focused mid-sized American city.