It was constructed in the 16th century following an original design by Michelangelo. At the beginning of the 18th century, Pope Clement XI commissioned the astronomer, mathematician, archaeologist, historian and philosopher Francesco Bianchini to build a meridian line, a sort of sundial, within the basilica. The sun shines through a small hole in the wall to cast its light on this line each day. At the summer solstice, the sun appears highest, and its ray hits the meridian line at the point closest to the wall. You can also see a wooden sculpture of Jesus with a face made of a true copy of the Turin canvas.