WASHINGTON, D.C. — The largest Catholic church in North America is now complete.

After 100 years of construction, thousands of worshippers Friday (Dec. 8) witnessed the blessing of 24 tons of Venetian glass that embellish the dome of the Basilica of the National Shrine of the Immaculate Conception.

Called the “Trinity Dome,” the glass mosaic is the final architectural element of the church, a shrine to Mary which sits next to the Catholic University of America and is visited by nearly 1 million people a year.

A 10-minute procession of cardinals, bishops, and priests preceded the two-hour ceremony and Mass to mark the dedication of the dome.

Washington Cardinal Donald W. Wuerl who celebrated the Mass called the basilica a “modern-day masterpiece.” Faith, he said, was the reason why so many people, for so many years, sacrificed to finish the church.

“Mary believed that nothing is impossible with God,” Wuerl said in his homily. “She is the supreme model of what it means to believe.”

The Trinity Dome is one of the largest mosaic installations of its kind in the world, composed of more than 14 million pieces of glass. It depicts the Holy Trinity, the Virgin Mary, a procession of saints and angels, the four evangelists and the Nicene Creed. It also includes stained-glass windows dedicated to the many donors to the dome.

The church for years has had scaffolding in the central nave to support work on the dome. Carol Wyble, a Catholic University graduate, once climbed it to watch her husband James, a mechanical engineer, work to bring things to a finish.

“It was quite a process,” said Wyble, who invited friends from New Hampshire to join in celebrating the newly completed basilica.

The dedication took place on Dec. 8, the Feast of the Immaculate Conception, which celebrates the belief that the conception of the Virgin Mary was free from original sin. The Roman Catholic Church teaches that the merits of Jesus kept Mary’s soul “immaculate.” The feast is a public holiday in many countries.

Pope Francis, who visited the basilica in 2015, sent a letter marking the dedication in which he expressed hope that all who look at the depiction of Mary in the dome may “with new vigor and new ardor of charity, show forth special love for the Church of Christ and the Gospel, even in our own age.”

Wuerl recalled that as a student in the 1960s he came to the basilica and all the walls except for one were simply brick.

“I thought it was magnificent then,” Wuerl told RNS, and said he was overcome with emotion during the procession. “Joy and thanks to God. I’m so joyful.”

Lawrence “Larry” Boesch of Potomac, Md., did not have to travel far to attend the Mass and dedication. A member of the Knights of Columbus, the world’s largest Catholic fraternal organization, he said he has watched the church grow since 1957. “It’s a place to come back to,” he said.

Others came from much farther to see the completed church.

Eric Gianforcaro, a religious studies major and senior at Cabrini University in Pennsylvania, said he has come many times before but he wanted to see Mother Cabrini depicted in the dome.

Chinyere Odoemene came from New Jersey with her sister-in-law who was visiting from Nigeria. Odoemene’s brother, a priest, brought her to the church in the 1990s, to help her heal from the loss of her husband. She said she returns as often as she can.

With the Washington basilica completed, the Basilica i Temple Expiatori de la Sagrada Familia in Barcelona, designed by the world famous architect Antoni Gaudi, is now the largest unfinished Roman Catholic church.

Next up for the basilica? Preparations have already begun for the upcoming 2020 celebration of the 100th anniversary of the placing of its foundation stone.