Before anyone owned a watch, someone still had to decide what time it was — and in the medieval world, that decision carried authority. In Europe, monasteries rang bells for the seven canonical hours of prayer, but by the late thirteenth century clockmakers had found a way to make falling weights release their energy one tick at a time: the verge-and-foliot escapement. Public clocks rose in Milan (1335), Genoa (1353) and dozens of other cities by 1400, and time began to shift, as historian Jacques Le Goff put it, from the Church's time to the merchant's time. In the Islamic world, five daily prayers whose windows were set by the sun made precise timekeeping a religious duty. From the late thirteenth century, mosques employed a muwaqqit, a professional astronomer-timekeeper; in Damascus, Ibn al-Shatir built a polar-axis sundial for the Umayyad Mosque in 1371/72 that read equal hours all year round, while engineers such as al-Jazari (1206) built elaborate water clocks like his famous elephant clock. In China, time belonged to the state: cities divided the day into 100 ke and the night into five watches sounded from drum towers, and in 1088–1094 Su Song built a forty-foot, water-driven astronomical clock tower in Kaifeng with an escapement and the oldest known endless chain drive. Meanwhile, incense clocks let ordinary households measure hours by a burning trail of powder. Three civilizations, one question: whose rhythm should everyone live by?