Summary: The petroglyphs on the endstone and the roofstone of Cairn T, Loughcrew, Ireland (dated c.3200 BC) are shown to be numeric pictograms, a quantitative picture writing. Each figure represents a number. By adding the numbers, the actual and true degrees of latitude of the landpoints they discovered are revealed in historical order. They discovered the Canaries, the Cape Verde Islands, Madeira, Rockall, the Azores, the Faroes, Iceland, and Greenland. So they tell the story of the unsuccessful attempts of megalithic people to cross the ocean in the north to the unknown other side of the world. Using these inscriptions as a mneumonic device, their aspirations and experiences were memorialized in this oldest written history on earth.