claims of al-Hasan, 'Ali's son. Al-Hasan made terms with Mu'awiya and died in 49, poisoned, it was commonly stated. The other son, al-Husayn, tried to enforce his claim, but met a tragic death at Kerbela. After al-Husayn's death some of the 'Alid partisans recognised Muhammad the son of 'Ali and al-Hanafiya as the fourth Imam; he, it is true, disowned these supporters, but that was a detail to which they paid no attention. His supporters were known as Kaysanites, and owed their origin to Kaysan, a freedman of 'Ali, who formed a society for the purpose of avenging the deaths of al-Hasan and al-Husayn. When this Muhammad died in 81 his followers divided into two sections, some accepting the fact of his death, others supposing that he had simply passed into concealment to appear again in due course. This idea of a "concealed" Imam was a heritage from the older religious theories of Persia and recurs again and again in Shi'a history. The important point is that both sections of this party continued to exist all through the 'Umayyad period, steadily refusing to recognise the official Khalifa as more than usurpers, and looking forward to the day when they could avenge the martyrdom of 'Ali and his sons.
We need not linger over the family of al-Hasan and his descendants. They were involved in 'Alid risings at Madina, and after the suppression of one of these in 169, long after the fall of the 'Umayyads, Idris the great-grandson of al-Hasan escaped to the far West and established a "moderate" Shi'ite
