In 1912, installation of mosaics in the interior began.
Completed in 1988, the mosaics collectively contain 41.5 million glass tesserae pieces in more than 7,000 colors.
Covering 83,000 square feet (7,700 m²), it is the largest mosaic collection in the world outside Russia.

While the mosaics in the side chapels and sanctuary walls were designed and installed by Tiffany Studios, the mosaics in the main cathedral areas were designed by August Oetken.
Installation of the mosaics was completed by dozens of artisans, including Hildreth Meiere, Ravenna Mosaic, Inc, and especially the father and son team, Paul and Arno Heuduck, who worked on the mosaic for nearly their entire working lives, and Emil Frei, Inc., of St. Louis.
The narthex of the church depicts the life of King Louis IX of France, namesake of the city and church, the rear dome includes mosaics of significant archdiocesan events, while the main dome by Jan Henryk de Rosen depicts Biblical scenes from both the Old Testament and New Testament.
In 1912, installation of mosaics in the interior began. Completed in 1988, the mosaics collectively contain 41.5 million glass tesserae pieces in more than 7,000 colors. Covering 83,000 square feet (7,700 m²), it is the largest mosaic collection in the world outside Russia.
While the mosaics in the side chapels and sanctuary walls were designed and installed by Tiffany Studios, the mosaics in the main cathedral areas were designed by August Oetken. Installation of the mosaics was completed by dozens of artisans, including Hildreth Meiere, Ravenna Mosaic, Inc, and especially the father and son team, Paul and Arno Heuduck, who worked on the mosaic for nearly their entire working lives, and Emil Frei, Inc., of St. Louis. The narthex of the church depicts the life of King Louis IX of France, namesake of the city and church, the rear dome includes mosaics of significant archdiocesan events, while the main dome by Jan Henryk de Rosen depicts Biblical scenes from both the Old Testament and New Testament.
Cathedral Basilica of Saint Louis (St. Louis)