Even before taking over Bahrain, the Qarmatians had instigated what some scholars have termed a 'century of terrorism' in Kufa. From Bahrain they launched raids along the pilgrim routes crossing Arabia: in 906 they ambushed the pilgrim caravan returning from Mecca and massacred 20,000 pilgrims. Under Abu Tahir al-Jannabi they came close to capturing Baghdad in 923, and sacked Mecca in 930. In the assault on Islam's holiest sites, the Qarmatians desecrated the Well of Zamzam with corpses of Hajj pilgrims, and took the Black Stone from Mecca to al-Hasa. According to historian al-Juwayni, the stone was returned 22 years later in 951 under mysterious circumstances. Wrapped in a sack, it was thrown into the Great Mosque of Kufa in Iraq, accompanied by a note saying "By command we took it, and by command we have brought it back." The theft and removal of the Black Stone caused it to break into seven pieces.