AMERICAN HISTORY is one of my favorite topics, so researching the material for this book was like going on a treasure hunt. I began my search believing, as most people do, that the Mason-Dixon Line had something to do with the Missouri Compromise and the Civil War. As I dug deeper, my perception changed considerably. I learned that individuals — ordinary folks like you and me — dared to cross many different kinds of boundaries, and in doing so shaped a nation. They prove that one person with a dream can change the world.

People I met during my research journey greatly enriched my story of the line. Todd Babcock steered me toward Moses McClean’s account book in the archives at the Historical Society of Pennsylvania. McClean’s lists added depth to the story and gave names to otherwise unknown crewmen. Todd patiently answered questions about surveying, as did Matthew Parbs and Robert Church at the National Museum of Surveying, in Springfield, Illinois. Surveyor and historian Jack Owens shed a clear, much-needed light onto the intricacies of running the Tangent Line and taught me how to use a level and a Gunter’s chain. Edwin Danson’s book Drawing the Line helped me understand the mystery of the Tangent Line. Craig Babcock took time from his busy back-to-college schedule and shared some of his experiences on the line. It’s likely that he has worked harder on the line and touched more of its boundary stones than any kid of his generation. At the American Philosophical Society, in Philadelphia, Roy Goodman kindly steered me through their Mason and Dixon files. Also in Philadelphia, Karie Diethorn took me upstairs at Independence Hall so I could see Dixon’s transit and equal altitude instrument. Deborah Warner, at the Smithsonian Institute, in Washington, D.C., explained how a zenith sector worked; she and Peter Marques, of Tentsmiths, provided me with information about eighteenth-century tents.

The Boundary Commissioners, the Calverts and Penns, and the governors of Pennsylvania and Maryland left a rich trail of documents. Deciding which snippets to include wasn’t easy, because I loved them all. In the end, I chose material that helped me better understand people and their reasons for pushing the boundaries of their world. Prior to researching this book, I thought William Penn was as dry as dust. After reading his writings and the transcript of his trial, I now see him as an earnest man of commitment, integrity, intelligence, honor, and dry wit. Period portraits and sketches put faces to the names of some folks in this book. Frustratingly, there are no images of Mason and Dixon. Before I began my research, in my mind’s eye I pictured them as old. I was startled when I realized that when Dixon began surveying the line, he was the same age my son was when he and I visited the Harlan farm and the Stargazer’s Stone. The ages of the boundary-line crewmen surprised me as well: a few were teenagers, and most were in their twenties or thirties.

At the fork of the Brandywine, Kate Roby graciously spent an afternoon showing my son and me around the Harlan house. She shared many family tales. Sitting in rooms that Mason and Dixon had often occupied, I understood why they kept coming back. Linda Kaat, who lives less than a stone’s throw from Joel Baily’s house, filled me in on the importance of taverns as colonial newsrooms.

Professor Janine Black and students Indiah Fortune, Amanda Veloz, and Matthew McDermott shared their modern-day quest for the location of the Plumstead-Huddle house, in Philadelphia. For them, one question started a journey of many twists, turns, and dead ends. But it was a journey that ultimately ended with the satisfaction of success. I agree with Matthew: you feel a special connection with the people of the past when you hold an old handwritten document. It’s a connection that erases time.

Stars are among the “stars” of this book. Matt Wiesner, at the observatory at Northern Illinois University, showed me a whole new world. Visiting the observatory on nights during different seasons helped me understand how Earth’s daily and annual rotations affect the stars we see. Perhaps most thrilling was watching the 2012 transit of Venus. It was an incredible coincidence that this astronomically rare event should occur while I was researching this book — and that I saw it, just like Mason and Dixon. Thankfully, no French warships sailed across Illinois’s horizons.

Seventeenth-century Maryland comes alive in Historic Saint Mary’s City. I easily imagined Leonard Calvert and the 1634 colonists disembarking from the Ark and Dove. A research trip to London took me to the Tower of London, where William Penn was imprisoned. I stood in the church where he was baptized and walked on the grounds where he played as a boy. Seeing Jeremiah Dixon’s circumferentor and the Shelton clock that Mason and Dixon used for their experiment in John Harlan’s garden helped me better understand how they worked. While being in London was exciting, my journey along part of the West Line was equally so. As my husband and I cleared stinging nettles away from one crown stone, we learned why the plant got its name — and not to touch it again. We walked some of the hilly terrain the crew had traveled — they definitely got their exercise! In one rural wooded area, I was afraid we might see a snake, but white-tailed deer were the only animals we encountered. (Being familiar with that area of Pennsylvania, I just know that Mason and Dixon must have seen at least one rattlesnake.)

I love letting my imagination roam as I meander in places like Saint Mary’s City, the fork of the Brandywine, and Philadelphia. On October 25, 2012, the 226th anniversary of Charles Mason’s death, I wandered among the gravestones in Christ Church Burial Ground. In all these places, a whisper of those who came before us lingers. These years-old whispers always inspire me. A million questions flood my mind. I have a burning desire to learn more. And so begins another adventure.

Although Mason and Dixon initially used a canvas observatory tent, carpenters soon constructed a more substantial wooden one, similar to this reconstruction set up at the Surveyors Rendezvous in August 2013. Instruments would have rested on stable bases constructed inside. The observatory was easily disassembled by removing the wood pegs. Wagons hauled the stacked wall and roof panels.