Ever seen a XVI or XCV label on something and been truly and totally confused? You're probably not alone, as the Roman numeral system is taught and used less and less these days.
In recent centuries, pretty much the entire world has transitioned over to the modern numeral system (also known as Arabic or Hindu-Arabic numerals), which uses 10 symbols (numbers 0 through 9) to make up all other numbers. Before that was created however, one of the primary numeral systems was created by the Romans. Unlike many other ancient systems, Roman numerals are still in use today, albeit in a limited capacity.
For example, Roman numerals are still used on a lot of clocks to indicate time, as well as books to identify chapter or page numbers. They're also employed quite a lot to indicate succession order, particularly with popes, kings, queens and the like. It'd be pretty weird to modernize Henry VIII to Henry 8, right? You don't have to be royalty to enjoy that honor, however. Any old person can be John Smith, IV for example, provided three other John Smiths preceded him in the family line.
Another common use for Roman numerals is for competitions, like the Super Bowl and the Olympic Games. Wars, like WWI and WWII, also use Roman numerals to distinguish them, and often monuments and buildings are engraved with the Roman numeral version of the year they were built. Filmmakers do the same thing at the end of film credits.
Roman Numeral Rules
Here's where Roman numerals get confusing for some people. Even though they're denoted "numerals," they're actually what we consider to be modern letters (I, V, X, L, C, D and M). Each one has a different value:
From there, Roman numeral users employ a set of fairly easy rules to indicate other numbers.
- If a larger number is followed by a smaller number, simply add the two together. For example, XI equals 11, because X is 10 and I is 1. So, 10+1 = 11.
- If the smaller number precedes the larger one, however, subtract it. For example, CD is 400 because C is 100 and D is 500. Since the smaller number is first, subtract it: 500-100 = 400.
- To keep numbers from getting out of control, the Romans decided that the same number can't be used more than three times in a row. (You may notice, however, that clocks and watches often do indeed use IIII to indicate the number 4 on timepieces using Roman numerals. Though there is no clear consensus as to why this is true, there are several interesting theories on the subject.) So, you can write this: XVIII, to indicate 18. However, another I can't be slapped on the end there, so 19 is XIX (X, which equals 10 comes first, followed by an I in front of an X, which is 9. So, X+IX is 10+9, which equals 19).
Limitations and History of Roman Numerals
Notice anything missing? Well, one of the primary reasons the Roman system became less relevant is that there's no way to denote zero. In mathematical calculations, this is a pretty big problem. So, as math progressed it became obvious that a more sophisticated system would be necessary.
Don't be too hard on the creators of Roman numerals, however. The system came into being way back in 500 B.C.E., and was used all around Europe until the modern numeral system was developed in 1300 C.E. So, things have clearly changed quite a bit, and people had to roll with the times and adapt as needed. For example, as the study of mathematics progressed, it became obvious that Roman numerals aren't the best for division or multiplication. The ripple effect of this thus affected more advanced computations and theories. There's also no easy or totally accurate way to express fractions using the Roman method.
Still, it's important to know the basics about Roman numerals. Although it's unlikely that you'll ever do math using them, it's likely that you will read books, clocks or watch the occasional Super Bowl. So, it's easier to have at least a basic grasp of what they are and how they're calculated.