Pilgrimage to the shrines of imams is a specific Shia custom, undertaken because Shia pilgrims believe that the imams and their relatives have the power to intercede with God on behalf of petitioners. Of the more than 1,100 shrines in Iran, the most important are those for the Eighth Imam, Ali al-Ridha, in Mashhad and for his sister Fatimah bint Musa in Qom, and for Seyyed Rouhollah Khomeini in Tehran. Each of these is a huge complex that includes the mausoleum of the venerated one, tombs of various notables, mosques, madrassas, and libraries.