Every year, millions of tourists, Colour Photoguide in hand, embark on a Rhine cruise. These tourists are touring not just picturesque historical landmarks but also the scene of interesting Nashequilibria. The castles and ruins mark the sites of former tolling stations along the Rhine Rivervalley. History records that at one time or another during the millennium 800-1800, 79 different locations served as toll booths along the Rhine and its tributaries . The Rhine River was the major commercial thoroughfare in Western Europe during this time, and Rhine customs and tolls were a major source of revenue for the Holy Roman Empire. As such, the Emperors closely guarded the right to collect tolls. Such a right could be granted only by the Emperor. For instance, one well-documented tolling station that operated continuously throughout the Middle Ages, Koblenz, first got this right in 1018. Formally, the right to collect a toll had to be renewed with each new Emperor, and
renewal was not automatic.