The curious case of the roman numeral IIII in clocks...

The substractive principle [applied to romal numerals] was used on and off in ancient times but was not regularly adopted until the Middle Ages. One interesting theory for the delay involves the simplest use of the principle-that of IV ("four"). These are the first letters of IVPITER the chief of the Roman gods and the Romans may have had a delicacy about writing even the begining of the name. Even today, on clockfaces bearing Roman numerals, "four" is represented as IIII and neves as IV. This is not because the clockface does not accept the substractive principles, for "nine" is represented as IX and never as VIIII.

Asimov on Numbers. Nothing Counts.

Isaac Asimov

Pocket Books, 1978

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