A storied friendship between two of America's founders--one that endured for fifty years--and the roadtrip that forged it. Between May 21 and June 6, 1791, Thomas Jefferson and James Madison went on a trip together through Upstate New York and parts of New England on horseback. This "northern journey" came at a moment of tension for the new nation, one in whose founding these Virginians and political allies had played key roles. The Constitution was ratified and President Washington was in his first term of office. Whether the country could overcome regional and political differences and remain unified, however, was still very much in question. Hence why some observers at the time wondered whether this excursion into Federalist New England by the two most prominent southern Democratic-Republicans, both future presidents, had an ulterior motive. Madison, maintained that the journey was for "health, recreation, and curiosity." He and Jefferson needed a break from their public responsibilities, so off they set. Along the way, they took notes on the ravages of the Hessian Fly, an insect that had been devastating wheat crops. While in Vermont, they focused on the sugar maple tree, which many hoped might offer a domestic alternative to slave-grown sugar cane imports. An encounter with a free Black farmer at Fort George resulted in a journal entry that illuminates their attitudes toward slavery and race. A meeting with members of the Unkechaug tribe on Long Island led to a vocabulary project that preoccupied Jefferson for decades, and which remains relevant today. The Northern Journey was also about friendship. Madison later recalled that the trip made Jefferson and him "immediate companions," solidifying a bond with almost no peer in the annals of American history, one that thrived for fifty years. Jefferson declared at the end of his life, that his friendship with Madison had been "a source of constant happiness" to him. This book reveals the moment when it took hold.