The unsanctioned race loops through Dorchester, Mattapan, Jamaica Plain and Roxbury. Run crews and community members gather to cheer on runners of all skill levels. And everyone gets to break the finish line tape.

Here is an overview of the toughest miles of the Boston Marathon course, according to several past and present runners.

Rachel Doucette is running the Boston Marathon to honor her fiancé, a permanently and totally disabled veteran. Doucette herself has lost approximately 170 pounds on her running journey.