If the numerals had their origin in India, as seems most probable, when did the Arabs come to know of them? It is customary to say that it was due to the influence of Mohammedanism that learning spread through Persia and Arabia; and so it was, in part. But learning was already respected in these countries long before Mohammed appeared, and commerce flourished all through this region. In Persia, for example, the reign of Khosr[=u] Nu['s][=i]rw[=a]n,[364] the great contemporary of Justinian the law-maker, was characterized not only by an improvement in social and economic conditions, but by the cultivation of letters. Khosr[=u] fostered learning, inviting to his court scholars from Greece, and encouraging the introduction of culture from the West as well as from the East. At this time Aristotle and Plato were translated, and portions of the _Hito-pad[=e]['s]a_, or Fables of Pilpay, were rendered from the Sanskrit into Persian. All this means that some three centuries before the great intellectual ascendancy of Bagdad a similar fostering of learning was taking place in Persia, and under pre-Mohammedan influences. {92} The first definite trace that we have of the introduction of the Hindu system into Arabia dates from 773 A.D.,[365] when an Indian astronomer visited the court of the caliph, bringing with him astronomical tables which at the caliph's command were translated into Arabic by Al-Faz[=a]r[=i].[366] Al-Khow[=a]razm[=i] and [H.]abash (A[h.]med ibn `Abdall[=a]h, died c. 870) based their well-known tables upon the work of Al-F[=a]zar[=i]. It may be asserted as highly probable that the numerals came at the same time as the tables. They were certainly known a few decades later, and before 825 A.D., about which time the original of the _Algoritmi de numero Indorum_ was written, as that work makes no pretense of being the first work to treat of the Hindu numerals. The three writers mentioned cover the period from the end of the eighth to the end of the ninth century. While the historians Al-Ma['s]`[=u]d[=i] and Al-B[=i]r[=u]n[=i] follow quite closely upon the men mentioned, it is well to note again the Arab writers on Hindu arithmetic, contemporary with Al-Khow[=a]razm[=i], who were mentioned in chapter I, viz. Al-Kind[=i], Sened ibn `Al[=i], and Al-[S.][=u]f[=i].