One place where you often see Roman numbers is on a clock face. The hours are marked as I to XII. However, there is something odd about these Roman numbers. If you look at four, it is IIII instead of IV. I think that this is because half of the numbers are upside down, since they follow the edge of the clock face round. You can get IV and VI muddled up when they're the right way up. It is even worse when they're upside down! IX and XI are not such a problem, since they are more or less the right way up. In fact, the Romans never had clocks like this, since they had not been invented. You can guess for yourself why the clock is showing the time "ten to three" in the following website. http://www.gwydir.demon.co.uk/jo/roman/number.htm

Romans *never* used "IV" for four. In fact IV is just six. They didn't care what order the letters went in. Four is IIII. Multiplication is easy when the order doesn't matter. So where did the idea of the IV for 4 come in? Oddly, not until the fourteen hundreds, long after Rome was sacked, as an abbreviation. So really, clockmakers have a choice of using the "correct" "IIII" or the more modern "IV". But "IIII" simply balances better than "IV" against the weighty "XVIII" on the other side of the clock face.

The reason that traditional Roman numeral clock faces display IIII instead of IV is because of the state of math skills when sundials were first numbered this way in ancient Rome. No joke. Ancient Romans numbered their sundials with numerals from their numbering system to mark the hours, and the average Roman citizen found it much easier to read the sundial in the town square by adding 4 one's than subtracting 1 from 5. Such was the state of Roman math skills. Since at the "extremes" of the day, that is early and late in the day when the sun was near the horizon, a sundial wasn't a very effective device, there were no numbers on the sundial representing times outside of 10am to 7pm or 8pm. So, this is why IX was not a problem. On modern faces, in keeping with this time-honored tradition (and watchmakers definitely want to honor time as much as possible, har-de-har-har...sorry), you'll still see IV marked as IIII. Since there was no tradition on sundials associated with 9, those are marked IX, as watches replaced sundials a good number of years later, after the number "zero" had been invented (discovered?) and people were no longer afraid of simple subtraction. This is a bit of trivia I learned from a book, "Why Do Clocks Run Clockwise and Other Imponderables?" (by Martin Feldman, I believe) just in case anyone wants to question my authority on this topic. :-)