Ten, by an X, which is two V’s joined at their points, and which two V’s represent the two hands.
Five tens are marked by an L; that is half the letter E, which is the same as C, the mark for a hundred.
Five hundred is marked by a D, half of the letter Φ, which is the same as M, the mark for a thousand.
According to this, the calculation of the Roman numbers was from five to five, that is, from one hand to the other. Ovid makes mention of this mode, as also of the number ten:—
“Hic numeris magno tunc in honore fuit.
Seu quia tot digiti per quos numerare solemnus,
Seu quia bis quino femina mense parit.
Seu quod ad usque decem numero crescente venitur:
Principium spatiis sumitur inde novis.”
Vitruvius also makes the same remark; he says, “Ex manibus denarius digitorum numerus.”
We have refined, however, upon the convenience which nature has furnished us with to assist us in our calculations; for we not only use our fingers, but likewise various figures, which we place in different situations, and combine in certain ways, to express our ideas.
Many unlettered nations, as the inhabitants of Guinea, Madagascar, and of the interior parts of America, know not how to count farther than ten. The Brasilians, and several others, cannot reckon beyond five; they multiply that number to express a greater, and in their calculations they use their fingers and toes. The natives of Peru use decimal progression; they count from one to ten; by tens to a hundred; and by hundreds to a thousand. Plutarch says, that decimal progression was not only used among the Grecians, but also by every uncivilized nation.