The original icon was an old Byzantine that has been dated variably from the 6th through the 9th century, thought to be the image that St. Luke painted of Madonna, known as the icon of San Sisto or the Madonna Advocata. Today this icon is in Monastero del Rosario on Monte Mario, while a copy can be seen on the altar of the nuns choir. You can read about the image's history on an inscription to the left of the main entrance.