Nine people were killed in a mass shooting at Emanuel AME Church, a historic black church located in downtown Charleston, South Carolina, Wednesday night.

Within hours, Charleston Police Chief Greg Mullen described the attack as a "hate crime."

It would have been a tragedy in the city — and the nation — in any context. But the specific story of Emanuel, an African Methodist Episcopal church that was added to the National Register of Historic Places in 1985, helps explain the unique devastation associated with the attack, as well as the near-immediate consensus that it was motivated by racism.

It was clear even before police identified the shooter as 21-year-old Dylann Roof — and without knowing much about his background — that a person set on terrorizing the city's African-American community by striking a symbolic blow, in addition to taking innocent lives, could not have chosen a target more steeped in history and meaning.

In remarks Thursday, President Obama called Emanuel "a sacred place in the history of Charleston and the history of America." The backstory of the church, summarized on its website, offers an overview that explains why.

1816: A new church for African Americans is formed

The church was founded in 1816 by a group of black former members of Charleston's Methodist Episcopal Church and led by Rev. Morris Brown, according to the church website. The African Methodist Church was an offshoot of the Free African Society, an organization founded in 1787 in Philadelphia.

1822: Burned in retaliation for the Denmark Vesey slave revolt

A CNN report explains the church was burned in 1822 after plans for a slave revolt organized by Denmark Vesey, one of the church's co-founders, were exposed. It was targeted because authorities suspected the church was the meeting place for planning the rebellion, which, according to the church, "created mass hysteria in throughout the Carolinas and the South."

In retaliation for their role in the plot, Vesey and five black people who were still enslaved were killed.

Notably, the slave revolt was planned for June 17, 1822. The attack on the church took place on the 193rd anniversary of this date.

1834: Secret worship despite racist laws

When all black churches were outlawed in 1834, the congregation, notes the AME church, worshiped underground "until 1865 when it was formally reorganized, and the name Emanuel was adopted."

1960s: A civil rights landmark

Black churches of all denominations played a pivotal role in the civil rights movement, serving as sources of leadership and centers of civil rights activism.

Because of Emanuel's historic significance, civil rights leaders made a point to visit it specifically. An image tweeted by the King Center shows Martin Luther King Jr. visiting the congregation.

Today: Charleston's largest black church

With room to seat 2,500, the church — which is known as "Mother Emanuel" — has the largest capacity of any black church in the city, and calls itself the oldest black AME church in the South.

In addition to listing times for Sunday service, church school, meetings for senior citizens, and seasonal and holiday events, its website invites the public to Bible study on Wednesday nights like the one on which the attack took place.