PARKLAND, Fla. — A former student opened fire with a semi-automatic rifle at a Florida high school Wednesday, killing at least 17 people in one of the nation's deadliest school shootings.

While some trace the modern history of school massacres to the Columbine High School shootings in Littleton, Colo., America's bloody history goes back much further than that. This timeline-map covers some of the most brutal mass-slayings in America's history, from Colonial times to the present.