For nearly 700 years, the Church has observed the Solemnity of the Most Holy Trinity, honoring one of the most powerful mysteries of our faith: the triune nature of our God. At the Basilica, the Trinity is portrayed in the central dome of the Great Upper Church, along with the Immaculate Conception, a litany of saints, angels, and apostles. The largest and final dome to be completed in the Great Upper Church, the Trinity Dome Mosaic spans a staggering 18,300 square feet.
As we celebrate the Solemnity of the Most Holy Trinity on June 4, we invite you to watch a collection of videos giving an inside look into the making of this magnificent piece of sacred art.
Designing the Mosaic
Designed by artisans at an Italian mosaic tile company called Travisanutto Giovanni, the Trinity Dome mosaic was created from 14 million pieces of glass. Each tile was initially shaped using a hammer and chisel and was created for a specific place on the mosaic, so if a tile broke incorrectly while being chiseled, the artisan had to take another piece of glass and begin the process again.
After the glass tiles were formed, they were temporarily affixed right side down on large sections of paper using a paste made from flour and water. This process ensured that when the mosaic was delivered to the Basilica for installation, artisans could cement the sections to the surface of the dome according to precise mapping. Over 24 tons of mosaic tiles were packed into wooden crates and shipped by air and boat from Italy to Washington, D.C. to be installed in the Trinity Dome.
Construction Preparations: Customized Scaffolding
Located approximately 159 feet above the sanctuary floor, the apex of the Trinity Dome was initially difficult for construction teams to access. Because the National Shrine remained open to the public during the installation, it was essential for crews to be able to work in the space without disrupting visitors. By partnering with the team at Rugo Stone, the Basilica was able to install a customized scaffolding system with advanced ventilation systems that was fully enclosed, which prevented dust and debris from entering the sanctuary and allowed construction workers to operate safely while the church remained open. Because it had to be raised inside the church, it had to be constructed without the use of a crane.
View the intricate process for yourself in the animation below.
Curing the Dome and Installing the Mosaic
Once the scaffolding was erected, the construction team set to work on their first task: to strip the ceiling of its original plaster coating, clean the roof tiles, and then recoat the ceiling with multiple layers of cement. This was rather difficult, because the mosaic design was created based on the measurements and thickness of the original plaster, so the new plaster had to be layered at the exact same depth to ensure that the mosaic could be properly installed into the space.
From start to finish, the Trinity Dome took over two years to complete and is the third dome on the path to the Christ in Majesty mosaic.
The Dedication of the Trinity Dome
On December 8, 2017, the Trinity Dome Mosaic was dedicated, marking the completion of the National Shrine according to its original architectural and iconographic plans. Described as the “crowning jewel” of America’s Catholic Church, the Trinity Dome mosaic features the Most Holy Trinity, the Blessed Virgin Mary under her title of the Immaculate Conception, a procession of saints, and the four evangelists, encircled by the Nicene Creed.
