Though Iran is known today as a stronghold of the Shi'a Muslim faith, it did not become so until much later, around the 15th century. The Safavid dynasty made Shi'a Islam the official state religion in the early sixteenth century and aggressively proselytized on its behalf. It is also believed that by the mid-seventeenth century most people in Iran had become Shi'as, an affiliation that has continued. Over the following centuries, with the state-fostered rise of a Persian-based Shi'ite clergy, a synthesis was formed between Persian culture and Shi'ite Islam that marked each indelibly with the tincture of the other.