saudi wahhabism is hostile to any reverence given to historical or religious places of significance for fear that it may give rise to 'shirk' (idolatry), and the most significant historic muslim sites (in mecca and medina) are located in the western saudi region of the hejaz. as a consequence, under saudi rule, an estimated 95% of mecca's historic buildings, most over a thousand years old, have been demolished for religious reasons. critics claim that over the last 50 years, 300 historic sites linked to muhammad, his family or companions have been lost, leaving fewer than 20 structures remaining in mecca that date back to the time of muhammad. demolished structures include the mosque originally built by muhammad's daughter fatima, and other mosques founded by abu bakr (muhammad's father-in-law and the first caliph), umar (the second caliph), ali (muhammad's son-in-law and the fourth caliph), and salman al-farsi (another of muhammad's companions).