Hard to believe but graffiti has been around for a staggering 30,000 years, from the prehistoric cave-paintings found in Burgundy, France, through to the gladiatorial fan-worship of Roman Lyon, and the messages left on the walls of the German Reichstag by Russian troops in 1945. Dr Richard Clay investigates the many reasons that compel people to scribble and scratch lasting mementos to their successors into any available surface, and reveals how these rudimentary memorials have developed into a legitimate art-form.