Why is Four o'clock IIII not IV on Roman Numeral Clocks?
It is thought that the normal use of IV may have been avoided as IVPPITER (Jupiter), the Roman king of the gods' name was often abbreviated to IV.
Whether true or not, Louis XIV of France preferred the use of IIII, and ordered that all clocks be made so, and the practice has remained. Certainly it looks more pleasing to the eye, as IIII balances better with the VIII denoting eight o'clock.
There is always an exception to a rule, though - the clock faces of 'Big Ben' show four o'clock as IV!