why do number four in roman numerals sometimes is also written as IIII instead of IV

In Roman numerals, the correct representation of the number four is indeed "IV". The use of "IIII" to represent four is a mistake that sometimes occurs due to misunderstanding or oversight.

However, there are two historical contexts where it might appear:

1. Variation in Early Usage: Early Roman numerals were not standardized and could vary greatly. Sometimes people would use a series of Vs or Is to represent numbers, rather than the more systematic approach we use today. So, for a while, "IIII" might have been used to represent four.

2. Clocks and Watches: On some old clocks and watches, you might see "IIII" instead of "IV". This was a design choice made by craftsmen, possibly to maintain symmetry and aesthetic balance on the face of the clock.

Despite these historical uses, "IV" is the correct and standard way to write the number four in Roman numerals. Modern usage always prefers "IV" over "IIII".