IIII or IV?

I thought the Ikea clock in our home was unique since its Roman numeral for 4 is IIII instead of IV. Then I found out it's normal! There are many theories why clocks with Roman numerals use IIII to represent 4... except the most famous clock, Big Ben that uses IV.

The theories range from reasons of symmetry, reference to Roman gods, kings, balance, etc. This site is an interesting read about why 4 is IIII and not IV, on clocks with Roman numerals, that is.