A Washington cardinal gave a blessing from scaffolding 159 feet above the ground in the Basilica of the National Shrine of the Immaculate Conception on Friday.

In front of an audience of builders, Church leaders, choir members and journalists, Cardinal Donald W Wuerl blessed the shrine’s Trinity Dome ahead of plans to install a new 24-ton mosaic composed of more than 14 million pieces of glass.

The mosaic, currently being built Travisanutto Giovanni in Spilimbergo, Italy, will be shipped to the shrine in 30,000 sections. It will depict the Trinity, Mary, 13 saints, the four evangelists and words from the Nicene Creed.