those letters of the alphabet which are generally used for figures; as I, one; V, five; X, ten; L, fifty; C, a hundred; D, five hundred; M, a thousand, &c.

It is not agreed how the Roman numerals originally received their value. 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, because it is the first letter of centum, which is Latin for 100. It has also been supposed, 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 denote 50. But what reason is there to suppose, that 1000 and 100 were the numbers which letters were first used to express? And what reason can be assigned why D, the first letter in the Latin word decem, ten, should not rather have been chosen to stand for that number, than for 500 because it had a rude resemblance to half an M? But if these questions could be satisfactorily answered, there are other numeral letters which have never yet been accounted for at all. These considerations render it probable, that the Romans did not, in their original intention, use letters to express numbers at all; the most natural account of the matter seems 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, I, they doubled, trebled, and quadrupled, to express 2, 3, and 4; thus, II. III. IIII. So far they could easily number the minims, or strokes, with a glance of the eye. But they presently found, that if more were added, it would soon be necessary to tell the strokes one by one: for this reason, when they came to 5, they expressed it by joining two strokes together in an acute angle thus, V; which will appear the more probable, if it be considered, that the progression of the Roman numbers is from 5 to 9, i.e. from the fingers on one hand to the fingers on the other.—Ovid has touched upon the original of this in his Fasti, lib. iii. and Vitruv. lib. c. i. has made the same remark.

After they had made this acute angle V, for five, they added the single strokes to it to the number of 4, thus, VI. VII. VIII. VIII. And then as the minims 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 this they doubled, trebled, and quadrupled, this double acute angle thus, XX. XXX. XXXX. They then, for the same reason which induced them first to make a single 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 50 was doubled, they then doubled the right angle thus D, to denote 100, and having numbered this double right angle four times, thus CCCC; when they came to the fifth number, as before, they reverted it, and put a single stroke before it thus I, to denote 500; and when this 500 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 CCC to denote 1000: when this note for 1000 had been four times repeated, they put down IXXX for 5000, IXXX for 10,000, and IXXX for 50,000, IXXX for 100,000, IXXX for 500,000, and IXXX for one million.

That the Romans did not originally write M for 1000, and C for 100, but square characters, as they are written above, we are expressly informed by Paulus Manutius; but the corners of the angles being cut off by the transcribers for dispatch, these figures were gradually brought into what are now numeral letters. When the corners of CXXX were made round, it stood thus CXXX, which is so near the Gothic n, that it soon deviated into that letter; so IXX having the corner made round, it stood thus IX, and then easily deviated into D. C also became a plain C by the same means; the single rectangle which denoted 50, was, without alteration, a capital L; the double acute angle was an X; the single acute angle a V consonant; and a plain single stroke, the letter I.; and thus these seven letters, M, D, C, L, X, V, I., became numerals.