Catholics across the nation took time to reflect on the tragedy of 9/11 as the country observed the 21st anniversary of the terror attacks that rocked the world.

“Dear police officers, firefighters, sheriffs and park rangers of our city of San Francisco: It is an honor for us to host you here… for this Mass in which we thank you for the sacrifices you make for us, sacrifices mostly which we do not even see,” Archbishop Salvatore Cordileone said in a Twitter post Sunday.

It was a message drawn upon by bishops across the country.

Bishop Donald J. Hying, of the Diocese of Madison, was one who made his sentiments known. "Think back to 2001, when our country was so unified in that horrific moment of suffering and of death, people came together, they helped strangers, it broke down barriers and in many ways significantly changed New York City” he said in a video message.

A group of leading U.S. bishops also addressed the topic.

“As we remember Sept. 11, 2001, let us reflect on Pope Francis' Prayer of Remembrance at Ground Zero in 2015,” the U.S. Conference of Catholic Bishops (USCCB) tweeted, sharing an excerpt from Pope Francis’ prayer from the Ground Zero Memorial during his visit to New York in September, 2015.  Pope Francis’ full prayer can be found here.

The attacks on the World Trade Center and the Pentagon were a subject of prayer and pastoral messages from the outset as the nation recovered.

On Nov. 14, 2001, the USCCB released a pastoral message document called “Living With Faith and Hope After September 11.” In it, the USCCB quotes the Beatitudes (Mt. 5:4,6,7,9) and said, “We offer words of consolation, criteria for moral discernment, and a call to action and solidarity in these troubling and challenging times.”

The bishops also honored the men and women, firefighters, police, chaplains and many others who sacrificed their lives. The document focuses on responding with faith and justice, and to further understand the role that religion can play in politics and specifically with terrorism. The USCCB emphasized the nation’s commitment to the common good, in unity with a determination to come together and defend America from all future threats, according to the pastoral message.

Last year, the Pillar released an article titled “The Catholic Church and 9/11” documenting stories and testimonials from that day. According to the Pillar, Pope St. John Paul II addressed the attacks on Sept. 12, 2002, and said “Christ’s word is the only one that can give a response to the questions which trouble our spirit. Even if the forces of darkness appear to prevail, those who believe in God know that evil and death do not have the final say.”

A prayer service was held at St. Patrick’s Cathedral in New York City 10 years after the attacks, with a Brooklyn pastor saying, “We decided to have exposition of the Blessed Sacrament. People flocked to the church… We held many funerals for police and fire persons who gave their lives,” the Pillar added.

For a different take on the attacks, Father Brian Jordan, a Franciscan Friar, tells the story of the Ground Zero Cross that survived the attack despite being in the middle of so much wreckage in this video.