Battle of Siffin
In 656, during the First Fitna, the Battle of Siffin, the decisive clash between Ali and the Umayyad Mu'awiya took place about west of Raqqa. The tombs of several of Ali's followers (such as Ammar ibn Yasir and Uwais al-Qarani) are in Raqqa and have become sites of pilgrimage. The city also contained a column with Ali's autograph, but it was removed in the 12th century and taken to Aleppo's Ghawth Mosque.