I fully believe that these places were places of healing and meditation, as in cathedrals are made in a sound amplifying manner, then later coopted by religion. When i studied music they told us that back in the middle ages, the frequency or tone they were singing in was raised to a higher pitch. Which i believe broke the healing effects. In the center of a sound bubble, you find a cross. https://youtu.be/whb5-_YMrwM&t=12m09s