public and openly propagated, but new members had to undergo an initiation ceremony involving seven stages. The Qarmatian world view was one where every phenomenon repeated itself in cycles, where every incident was replayed over and over again. 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. The sack of Mecca followed millenarian excitement among the Qarmatians (and in Persia) over the conjunction of Saturn and Jupiter in 928. Bahrain became the seat of the Qarmatian Mahdi-Caliph from Isfahan who abolished Sharīa law. The new Mahdi also changed the qibla of prayer from Mecca to that of fire, a specifically Zoroastrian practice. Some scholars take the view that "they may not have been Isamailis at all at the outset, and their conduct and customs gave plausibility to the belief that they were not merely heretics but bitter enemies of Islam." For much of the 10th century the Qarmatians were the most powerful force in the Persian Gulf and Middle East, controlling the coast of Oman, and collecting tribute from the Abbasid caliph in Baghdad and from the rival Ismaili Fatimid caliph in Cairo, whom they did not recognize. The land they ruled over was extremely wealthy with a huge slave-based economy according to academic Yitzhak Nakash: The Qarmatian state had vast fruit and grain estates both on the islands and in Hasa and Qatif. Nasiri Khusru, who visited Hasa in 1051, recounted that these estates were cultivated by some thirty thousand Ethiopian slaves. He mentions that the people of Hasa were exempt from taxes. Those