In 1563, Michelangelo used a section of what remained of the Baths of Diocletian to house Santa Maria degli Angeli e dei Martiri. What I like about the vaulted transept space shown here is that, while standing in it, one can feel the grandeur and immense scale of the spaces within the Roman baths.
Noted on the drawing is the meridian solar line, which was commissioned by Pope Clement XI in the 18th century to verify the accuracy of the Gregorian calendar. Astronomer and mathematician Francesco Bianchini installed the brass line across the floor of the church at longitude 12°30’E. At noon each day, the sun, if it is out, shines through a small hole in the south wall to cast its light on the line, marking the progress of the sun through the year.