As a political project, Zaydism had been implemented in the ninth century in the form of two main Zaydi states in two distant locations. The first was established by Hasan ibn Zayed in 864 in historical Tabaristan, south of the Caspian Sea, but its political and ideological impact was marginal. This Zaydi state only lasted until 928. Four decades later, it was revived in Gilan along the Caspian Sea and survived until 1126. By the fifteenth century, the majority of Zaydi communities in the Caspian region had converted to Twelver Shi‘ism