Clock faces usually move clockwise because that is the direction a sundial's shadow travels in the north.

The longer version

In the Northern Hemisphere the shadow on a horizontal dial sweeps from west toward north and then east as the day advances, which traces a path running left to right across the upper face. Early clockmakers simply copied the motion people already expected. The Sun appears to travel across the sky in the same sense.

Nothing about gearing requires that direction; a mirror-image mechanism would work just as well. The convention became fixed once dials were mass-produced, and reversing it would now confuse everyone. Curiously, the hands move with the shadow only on dials facing upward, since vertical wall dials mounted in the south can sweep the other way.

Where this entry sits

These facts wander through clocks, calendars, time zones, and the long human effort to measure passing hours. You will find leap years, odd month lengths, ancient sundials, and the reasons modern timekeeping works the way it does. The full list sits on the Time and Calendars page, where every entry is listed in order.