In typography, the style of numeral used exclusively until about the tenth century A.D. The Romans—generally speaking—used letters as numbers, such as I (1), V (5), X (10), L (50), C (100), D (500), and M (1,000), but the co-opting of the alphabet to stand in for the number system didn't begin that way. For example, it is believed that the symbol V for 5 was merely representative of an open hand with the fingers held together and the thumb apart, kind of like the Vulcan salute, while the X for (10) is merely a double V, or two crossed hands. The original symbol for 1,000 was a circle with a vertical line through it (similar to the Greek letter phi??), and the D for 500 is believed to have been simply one-half of this symbol. The original symbol for 100 was a circle with a horizontal line through it (similar to the Greek letter theta??"]). The use of C and M may have come from the first letters of the words centum (meaning "100") and mille ("1,000").
Numbers between these main numbers were typically additive; II was 2, III was 3, VI was six, XI was 11, CI was 101, etc. The subtractive principle came about later; VIIII was often used for 9 in ancient Rome, while today IX is. The Romans were not a mathematically-inclined people, so large numbers were rarely called for.
Roman numerals are typeset just like capital letters are. The front matter of many books is typically paginated using lowercase Roman numerals (i, ii, iii, iv, etc.).
At the beginning of the second millennium A.D., the so-called Arabic numerals (actually of Indian origin) were introduced into Western Europe, and within a few centuries proponents of the new numerals defeated those of Roman numerals and by the beginning of the fifteenth century were becoming widely used. (See also Arabic Numerals.)