Art historian Dr Richard Clay traces the impulse to mark walls back to the painted caves of France, then follows it forward through Roman latrines scrawled with insults, medieval church graffiti, and political slogans daubed on city streets, arriving at the spray-painted murals of contemporary street art. He argues that graffiti has never been a single thing, sometimes vandalism, sometimes protest, sometimes the only historical record left by people with no other way to leave a mark. Clay visits sites where centuries-old scratched inscriptions survive alongside modern tags, treating both as evidence of the same basic urge. The film moves between ancient ruins and present-day cities, using close shots of carved and painted surfaces to make the case that today's street artists are working in a tradition thousands of years old rather than inventing something new. It closes by asking what separates crime from art, and lets the historical record answer instead of a single talking head.