The Night of Power commemorates the first revelation, and the Quran devotes a short sura to it that says it is better than a thousand months — approximately eighty-three years. The date is deliberately unspecified. Hadith point to the last ten nights, and especially the odd ones, with the twenty-seventh most commonly favoured, but the concealment is the mechanism: the only reliable way to catch it is to keep several nights, which is exactly what the tradition wants. Many Muslims perform itikaf during the last ten days, secluding themselves in the mosque, sleeping there, and doing nothing but pray and recite. Mosques stay open all night and fill; in Mecca the crowd on the twenty-seventh is one of the largest of the year. It is the one night when even irregular practitioners often show up.