The shrine at Mashhad holds the tomb of Ali al-Rida, the eighth Imam of Twelver Shia Islam, who died in 818. The complex around it has grown into one of the largest religious sites in the world, with mosques, courtyards, libraries and a museum, and is administered by the Astan Quds Razavi foundation. It receives pilgrims in numbers reported in the tens of millions each year, which makes it the most visited pilgrimage destination in Iran.