In 1763, Charles Mason and Jeremiah Dixon began a survey of the region of North America around the Pennsylvania border. Although intended as a solution to a land-ownership dispute, their work wound up as a component of the conflicts, a century later, that resulted in the American Civil War. But an additional, unexpected consequence of their work was the first experimental measurement of the mass of the Earth! This took place thirty years before rigorous experiments were conducted on the topic. In this presentation, I will discuss how the remarkable precision of 18th century surveying and the scientific rigor of two surveyors led to this often-overlooked discovery.