It has been supposed that the Romans used M to denote 1000 because it is the first letter of Mille, which is Latin for 1000; and C to denote 100, it being the first letter of Centum, the Latin term for 100. Some also suppose that D, being formed by dividing the old M in the middle, was therefore appointed to stand for 500,—that is, half as much as the M stood for when it was whole; and that L being half a C, was, for the same reason, used to denominate 50. But the most natural account of the matter appears to be this:—
The Romans probably put down a single stroke, Ⅰ, for one, as is still the practice of those who score on a slate, or with chalk; this stroke they doubled, trebled, and quadrupled, to express two, three, and four: thus, ⅠⅠ, ⅠⅠⅠ, ⅠⅠⅠⅠ. So far they could easily number the strokes with a glance of the eye; but they found that if more were added it would be necessary to count the strokes one by one: for this reason, when they came to five, it was expressed by joining two strokes together in an acute angle, thus, Ⅴ.
After they had made this acute angle, Ⅴ, for five, they then added single strokes to the number of four, thus, ⅤⅠ, ⅤⅠⅠ, ⅤⅠⅠⅠ, ⅤⅠⅠⅠ, and then, as the strokes could not be further multiplied without confusion, they doubled their acute angle by prolonging the two lines beyond their intersection, thus, Ⅹ, to denote two fives, or ten. After they had doubled, trebled, and quadrupled this double acute angle, thus, ⅩⅩ, ⅩⅩⅩ, ⅩⅩⅩⅩ, they then, for the same reason which induced them to make a single angle first, and then to double it, joined two single strokes in another form, and, instead of an acute angle, made a right angle, Ⅼ, to denote fifty. When this was doubled, they then doubled the right angle, thus, ⊏, to denote one hundred, and, having numbered this double right angle four times, thus, ⊏⊏, ⊏⊏⊏, ⊏⊏⊏⊏, when they came to the fifth number, as before, they reverted it, and put a single stroke before it, thus, Ⅰ⊐, to denote five hundred; and, when this five hundred was doubled, then they also doubled their double right angle, setting two double right angles opposite to each other, with a single stroke between them, thus, ⊏Ⅰ⊐, to denote one thousand: when this note for one thousand had been repeated four times, they then put down Ⅰ⊐⊐ for five thousand, ⊏⊏Ⅰ⊐⊐ for ten thousand, and Ⅰ⊐⊐⊐ for fifty thousand.
The corners of the angles being cut off by transcribers for despatch, these figures were gradually brought into what are now called numerical letters. When the corners of ⊏Ⅰ⊐ were made round, it stood thus, ⅭⅠↃ, which is so near the Gothic ന that it soon deviated into that character; so that Ⅰ⊐ having the corners made round stood thus, ⅠↃ, and then easily deviated into D. ⊏ also became a plain C by the same means: the single rectangle, which denoted fifty, was, without any alteration, a capital L; the double acute angle was an X; the single acute angle, a V; and a plain single stroke, the letter I. And thus these seven letters, M, D, C, L, X, V, I, became numerals. As a further proof of this assertion, let it be considered that ⅭⅠↃ is still used for one thousand, and ⅠↃ for five hundred, instead of M and D; and this mark, ന, is sometimes used to denote one thousand, which may easily be derived from this figure, ⊏Ⅰ⊐, but cannot be deviations from, or corruptions of, the Roman letter M. The Romans also expressed any number of thousands by a line drawn over any numeral less than one thousand: thus, V̅ denotes five thousand, L̅X̅ sixty thousand; so, likewise, M̅ is one million, M̅M̅ two millions, &c.
Upon the discovery of printing, and before capitals were invented, small letters served for numerals; not only when Gothic characters were in vogue, but when Roman had become the prevailing character. Thus, in early times, i b x l c d m were, and in Roman type are still, of the same signification as capitals when used as numerals. Though the capital J is not a numeral letter, yet the lower-case j is as often and as significantly used as the vowel i, especially where the former is employed as a closing letter, in ij iij bj bij biij dcij, &c. In Roman lower-case numerals, the j is not regarded, but the i stands for figure 1 wherever it is used numerically.
During the existence of the French Republic, books were dated in France from the first year of the Republic: thus An. XII. (1803,) or twelve years from 1792.
ARITHMETICAL FIGURES.
The arithmetical or Arabic numerals are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. Properly they should be styled Hindu or Indian numerals; for the Arabs borrowed them, along with the decimal system of notation, from the Hindus. They were probably first introduced from the East into Italy about 1202; yet they did not come into general use before the invention of printing. Accounts were kept in Roman numerals up to the sixteenth century. Figures are usually made one en thick; but of late a broader figure is cast for newspaper use, which is two-thirds or six-sevenths of an em in width.