This beautiful mosaic depicting the angels Raphael and Gabriel flanking Jesus dates back to 545. It's part of the large collection of Byzantine art at the Bode Museum. This particular piece comes from Ravenna, a city on the UNESCO World Heritage list for its many early Christian mosaic pieces (like this one).
Here's a better look at how the apse mosaic is presented in the room. I know this is not exactly a mural, but I think it's close enough. You'll find more of them at Monday Mural.