Historic National Prayer Service held at Washington National Cathedral for victims of the September 11 attacks. A similar service is held in Canada on Parliament Hill, the largest vigil ever held in the nation's capital.

The Cathedral Church of Saint Peter and Saint Paul in the City and Episcopal Diocese of Washington, commonly known as Washington National Cathedral or National Cathedral, is a cathedral of the Episcopal Church. The cathedral is located in Washington, D.C., the capital of the United States. The structure is of Neo-Gothic design closely modeled on English Gothic style of the late fourteenth century. It is the second-largest church building in the United States, and the third-tallest building in Washington, D.C. The cathedral is the seat of both the presiding bishop of the Episcopal Church and the bishop of the Episcopal Diocese of Washington. Over 270,000 people visit the structure annually.

The September 11 attacks, also known as 9/11, were four coordinated Islamist terrorist suicide attacks by al-Qaeda against the United States in 2001. Nineteen terrorists hijacked four commercial airliners, crashing the first two into the Twin Towers of the World Trade Center in New York City and the third into the Pentagon in Arlington County, Virginia. The fourth plane crashed in a rural Pennsylvania field during a passenger revolt. The attacks killed 2,977 people, making it the deadliest terrorist attack in history. In response to the attacks, the United States waged the global war on terror over multiple decades to eliminate hostile groups deemed terrorist organizations, as well as the governments purported to support them.

Parliament Hill, colloquially known as The Hill, is an area of Crown land on the southern bank of the Ottawa River that houses the Parliament of Canada in downtown Ottawa, Ontario. It accommodates a suite of Gothic revival buildings whose architectural elements were chosen to evoke the history of parliamentary democracy. Parliament Hill attracts approximately three million visitors each year. The Parliamentary Protective Service is responsible for law enforcement on Parliament Hill and in the parliamentary precinct, while the National Capital Commission is responsible for maintaining the nine-hectare (22-acre) area of the grounds.