Heartbreak Hill is located between miles 20 and 21 of the Boston Marathon course. It is the last and most famous of the Newton Hills, beginning just after the 20-mile mark and stretching for about half a mile (approximately 0.6 miles or 800 meters) with a gradient around 3.3% to 5%
. This hill is notable because it comes late in the race when runners are already fatigued, making it particularly challenging despite its moderate incline. The top of Heartbreak Hill is near mile 21, after which the course begins a downhill stretch toward the finish
