Answer: On Clock Faces

Roman numerals are placed from left to right, in order of value, starting with the largest numeral first. In cases where this would yield four characters in succession (such as the transition from III for 3 to IIII for 4) the traditional method is to use subtractive notation where in the 4 is represented as IV (or 1 subtracted from 5).

The only place you’ll find the rule broken is on clock faces. The traditional arrangement on a clock face whose numbers are designated with Roman numerals is to display the 4 as IIII. While this tradition cannot be traced to a single moment in history, a wide variety of events conspired to make IIII the most popular designation.

The the Wells Cathedral Clock (one of the earliest surviving mechanical clock towers) featured IIII (most likely taken from the enumeration systems of contemporary manuscripts). King Louis the XIV of France preferred his clocks with the IIII and he ordered all his clock makers to build the clocks in such a fashion. Further, using IIII instead of IV creates a pleasing visual symmetry with the opposing VIII (8 O’Clock). Practically speaking, however, the most likely source of the deviation is the clockmakers themselves–using IIII in place of IV requires fewer molds for the numerals.