One of the most notable features of the site is the Green Dome over the center of the mosque, where the tomb of Muhammad is located. It is not exactly known when the green dome was constructed but manuscripts dating to the early 12th century describe the dome. It is known as the Dome of the Prophet or the Green Dome. Subsequent Islamic rulers greatly expanded and decorated it. Early Muslim leaders Abu Bakr and Umar are buried in an adjacent area in the mosque.