For thousands of years, people of all cultures have made and used clocks, from the city sundials of ancient Rome to the medieval water clocks of imperial China, hourglasses fomenting revolution in the Middle Ages, the Stock Exchange clock of Amsterdam in 1611, Enlightenment observatories in India, and the high-precision clocks circling the Earth on a fleet of GPS satellites that have been launched since 1978. Clocks have helped us navigate the world and build empires, and have even taken us to the brink of destruction. Elites have used them to wield power, make money, govern citizens, and control lives?and sometimes the people have used them to fight back.