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.