It is at this point that a further discovery of Prof. Clay has furnished us with the necessary data for a decision. Among the tablets of the Yale Babylonian Collection he has come across several documents of Rîm-Sin's reign, which bear a double-date. In every case the first half of the double-date corresponds to the usual formula for the second year of the Nîsin era. On two of them the second half of the date-formula equates that year with the eighteenth of some other era, while on two others the same year is equated with the nineteenth year.[20] It is obvious that we here have scribes dating documents according to a new era, and explaining that that year corresponds to the eighteenth (or nineteenth) of one with which they had been familiar, and which the new method of time-reckoning was probably intended to displace. Now we know that, before the capture of Nîsin, the scribes in cities under Rîm-Sin's control had been in the habit of dating documents by events in his reign, according to the usual practice of early Babylonian kings.[21] But this method was given up after the capture of Nîsin, and for at least thirty-one years after that event the era of Nîsin was in vogue.[22] In the second year of the era, when the new method of dating had just been settled, it would have been natural for the scribes to add a note explaining the relationship of the new era to the old. But, as the old changing formulæ had been discontinued, the only possible way to make the equation would have been to reckon the number of years Rîm-Sin had been upon the throne. Hence we may confidently conclude that the second figure in the double-dates was intended to give the year of Rîm-Sin's reign which corresponded to the second year of the Nîsin era.
It may seem strange that in some of the documents with the double-dates the second figure is given as eighteen and in others as nineteen. There is more than one way in which it is possible to explain the discrepancy. If we assume that the conquest of Nîsin took place towards the close of Rîm-Sin's seventeenth year, it is possible that, during the two years that followed, alternative methods of reckoning were in vogue, some scribes regarding the close of the seventeenth year as the first year of the new epoch, others beginning the new method of time-reckoning with the first day of the following Nisan. Rut that explanation can hardly be regarded as probable, for, in view of the importance attached to the conquest, the promulgation of the new era commemorating the event would have been carried out with more than ordinary ceremonial, and the date of its adoption would not have been left to the calculation of individual scribes. It is far more likely that the explanation is to be sought in the second figure of the equation, the discrepancy being due to alternative methods of reckoning Rîm-Sin's regnal years. Again assuming that the conquest took place in Rîm-Sin's seventeenth year, those scribes who counted the years from his first date-formula would have made the second year of the era the eighteenth of his reign. But others may have included in their total the year of Rîm-Sin's accession to the throne, and that would account for their regarding the same year as the nineteenth according to the abolished system of reckoning.[23] This seems the preferable explanation of the two, but it will be noticed that, on either alternative, we must regard the first year of the Nîsin era as corresponding to the seventeenth year of Rîm-Sin's reign.