There were several of these semi domes over large side chapels off the nave.
Best to view in "Original" because other versions resized by Pbase are decidedly unsharp.
*****
We met up with fellow Pbaser Long Bach Nguyen and his wife Katherine at this beautiful basilica, which although located fairly close to our house, we hadn’t visited since 2008. A lot of finishing touches have been made since then, and it was nice to see it in its completed state as well as to meet Long and Katherine.
The Basilica of the National Shrine of the Immaculate Conception is the largest Catholic church in the United States and in North America and the tallest habitable building in Washington, D.C. The foundation stone was laid in 1920, and the mosaic adornment of final dome was completed in 2017.
Getting’ outta there, posted earlier: