Christensen, by the following reasoning, comes to the conclusion, that it was written somewhere between 557 and 570. Among the sources of our knowledge of the Sasanian institutions, one of the most important is the letter of Tansar to the king of Tabaristan published and translated by Darmesteter in the _Journal Asiatique_ (1894). The information which it gives on points where we can verify it is so exact that we cannot doubt that the letter was composed in the time of the Sasanians. On the other hand, on the first reading of the epistle I formed the impression that it was a literary fiction dating from the time of Khusro when the tradition made of Ardeshir the model of political sagacity and the founder of the entire organisation of the empire. The letter impressed me as a historical, theological, political and moral dissertation which in the shape of a correspondence between the grand Herbed Tansar and the king of Tabaristan, ill-informed regarding the new state of affairs and hesitating to submit himself to Ardeshir, was calculated to instruct contemporaries. It, therefore, fits in with the entire literature of the _Andarz_ type, which was developed under Khusro and the object of it was the moral instruction of the people. A more minute examination has confirmed me in this view and now I think I am able to affirm positively that the letter was composed under Khusro I. Tansar relates that Ardeshir softened the penalties for crimes against the religion. Formerly, "they used to put to death without hesitation those who set aside the religion of the State. But Ardeshir has directed that the accused shall be arrested and shall be catechised during a year and only if that proves of no effect he shall be killed." As a matter of fact, the rigorous ordinance which awarded the punishment of death for apostacy could not have existed before Parsism became with Ardeshir the State religion. The relaxation of punishment, on the other hand, dates from a much later period, when the standpoint of greater humanity began to be prevalent and when it was attempted to give greater authority to these views by attributing them to the celebrated founder of the dynasty. And we can say the same thing with reference to the less severe punishment for crimes committed against the State and in respect of other things mentioned in the letter. Besides, the tolerance in matters religious and the humanity of Khusro I are well-known.