The District of Columbia is a diamond-shaped square, ten miles on a side. In 1791-92 Andrew Ellicott, with Benjamin Banneker and colleagues, slashed through the wilderness, surveyed the bounds of the Federal City, and placed marker stones every mile along the edge. Many of these forty historic stones yet survive. My self-imposed quixotic mission: visit them, photograph them, and record their GPS coordinates. Here's a Google Map of the results. Click on a marker to get high-resolution imagery and a locator map for that stone.