The sinuous border that separates the U.S. from Canada is known as the 54th parallel, though the bulk of the boundary is directly defined by other geographical markers. Spanning over 5,525 miles, it's often cited as the longest international border between two countries. The border traverses diverse landscapes, including mountains, prairies, and forests. Several agreements, including the Rush-Bagot Treaty and the Webster-Ashburton Treaty, have defined its shape over the years, fostering cooperation between the two nations.