WASHINGTON — Churchgoers around the United States marked the 17th anniversary of the 9/11 terrorist attacks with moments of silence, special prayer services and Masses.

In Brooklyn, N.Y., a Mass for fallen heroes was celebrated at the Co-Cathedral of St. Joseph Sept. 11. The Mass followed a procession of firefighters from across the country who first gathered at ground zero in Lower Manhattan, where the twin towers of the World Trade Center once stood. They marched in single file across the Brooklyn Bridge carrying 23 ceremonial flags of the New York City Fire Department. Each flag represented one of 23 firefighters from Battalion 57 in Brooklyn killed in the line of duty at the trade center.

The journey from ground zero to Brooklyn served “to symbolically bring the brothers back home,” organizers said.

Official ceremonies took place at the sites in New York, Virginia and Pennsylvania where four hijacked planes crashed 17 years ago, claiming the lives of 2,996 people (including 19 hijackers).

Two planes flew into the World Trade Center in New York, bringing down the twin towers and killing office workers and other staff in the buildings, emergency first responders and people fleeing in the streets.

Another plane crashed into the Pentagon in Virginia, just outside Washington, and a fourth airliner went down in a field near Shanksville, Pa.

President Donald Trump spoke at anniversary ceremonies at the Flight 93 National Memorial near Shanksville. Vice President Mike Pence addressed a crowd at the Pentagon.

Attending a meeting of the U.S. bishops’ Administrative Committee Sept. 11 in Washington, New York Cardinal Timothy M. Dolan said he and his brother bishops remembered the people who perished and their families at a Mass at the U.S. bishops’ conference headquarters.

He wrote in a statement a week earlier about historic St. Peter’s Church in downtown New York, which had “served as a sanctuary, first-aid station, hospice, relief center and even a mortuary” on 9/11 and for many days afterward.

At a Mass this year at St. Peter’s, Cardinal Dolan stated the congregation “prayerfully remembered with sorrow, reverence and love those who had perished that unforgettable day, and their families who still grieve, along with those who have since lost their lives due to illnesses contracted during the rescue and recovery efforts that followed.”

Cardinal Dolan recalled his first 9/11 anniversary observance nine years ago as recently installed archbishop of New York, also held at St. Peter’s.

“Never will I forget the wise comment of the pastor at the time, Father Kevin Madigan,” Cardinal Dolan said. The priest told him: “9/11 was Good Friday again here in New York; but the story we need to remember is actually 9/12, a real Easter, as this community rose in rescue, relief, support, rallying and rebuilding.”

In 2015, Pope Francis visited the site of the 9/11 attacks in Lower Manhattan, where grief remained “palpable,” he said.