The Muslims transformed half of St. John's Church into the city's Friday Mosque (Great Mosque of al-Nuri) and Homs soon became a centre of Islamic piety since some 500 companions of Muhammad settled there after its conquest. The tombs of Khalid ibn al-Walid, his son Abd al-Rahman, and Ubayd Allah, the son of Caliph Umar are located in the city. During the conflict between the Umayyads and Ali, the inhabitants of Homs allied themselves with Ali and when the latter was defeated, the Umayyad caliph Mu'awiyah hived the northern half of Jund Hims to form a separate district, Jund Qinnasrin, apparently as punishment. Ali's oratory ("mash-had 'Ali") was located in the city, and Islamic tradition claims his fingerprints are engraved on it. Despite repression by the Umayyads, Homs remained a center of Shia Islam for a while longer. As a stronghold of the Banu Kalb, the city became involved in the latter's conflicts with the Qays tribal faction. The last Umayyad caliph, Marwan II, enjoyed the support of the Qais and subsequently razed the city walls in response to a rebellion by the Banu Kalb.