BOOK I.

is the mother and author of all numbers; and which, often taking on the nature of a number, Arithmeticians do not fear to count among numbers and call a number. This doubled generates two; and where it is added to two, it produces three; and added to three, four; and in this way, it generates all numbers, so that advancing in a natural series, they surpass each other by a monad. Wherefore one, the one and first of the digits, as we remembered above, added to nine, which is the greatest of the digits, makes ten, 10, or a DECURY: which Vitruvius calls Decussim, and the Greeks call Dekada decade. This is the first of the articles, a most perfect number, as will be recognized from those things which we are about to relate concerning it, and which Aristotle in his Problems, Vitruvius, Augustine, and others have mentioned. From ten and the same digits repeated, eleven, 11, twelve, 12, and other composite numbers are composed, until another decade is made. Which, with the previous decury, becomes the number called Twenty, 20, a name composed of twice and ten. By the same ratio, other decuries of monads are produced up to the tenth, that is, ten tens: which are called by the Latins A HUNDRED, 100, and a CENTURY, and by the Greeks Hecaton and hekatontas a hundred. Afterwards, other hundreds are added: until these also are equal in number, that is, ten. Which ten centuries, or ten hundreds, are called by the Latins a THOUSAND, and by the Greeks chilioi thousands and chilias a thousand, 1000. And these thousands are repeated: and become two thousand, 2000, three, four, and others up to ten thousand, 10000. Which article the Latins do not have in one word,