On the other hand, it is also quite evident that the treatise can not have been written after the great revision of the Norwegian laws which was carried out during the reign of Magnus Lawmender. The new court-law, which was promulgated about 1275, is clearly later than the _Speculum Regale_: the fine exacted for the death of a king’s thegn, which is given as forty marks in the _King’s Mirror_, is fixed at a little more than thirteen marks in Magnus’ legislation. In 1273 the law regulating the succession to the throne made impossible the recurrence of joint kingships; but the principle of this arrangement appears to have been accepted as early as 1260, when the king’s son Magnus was given the royal title. Another decree, apparently also from Hakon’s reign, which abolished the responsibility of kinsmen in cases of manslaughter and deprived the relatives of the one who was slain of their share in the blood fine, also runs counter to methods described in the _King’s Mirror_, which states distinctly that kinsmen share in the payment.[139] It is therefore safe to conclude that the work was written some time between 1217 and 1260.
The earliest attempt to date the _King’s Mirror_ was made by the learned Icelander, Hans Finsen. In an essay included in the Sorö edition (1768) he fixes the time at about 1164.[140] J. Erichsen, who wrote the introduction to this edition, doubts that it was composed at so early a date; impressed with the fact that the work reflects the political views of the Birchshank faction, he is inclined to place the date of composition some time in Sverre’s reign or in the last decade of the twelfth century.[141] The striking resemblance between the ideas expressed in the treatise and the guiding principles of Sverre’s regime led the editors of the Christiania edition to the same conclusion: 1196 or soon after.[142] And so it was held that the work is a twelfth century document until a Danish artillery officer, Captain Otto Blom, began to make a careful study of the various types of weapons, armor, and siege engines mentioned in the work. His conclusion, published in 1867, was that the _King’s Mirror_ reflects the military art of the thirteenth century and that the manuscript was composed in the latter half of the century, at any rate not long before 1260.[143] This conclusion has been accepted by Gustav Storm,[144] Ludvig Daae,[145] and virtually all who have written on the subject since Blom’s study appeared, except Heffermehl, whose belief that Ivar Bodde was the author could not permit so late a date, as Ivar, who was a man of prominence at Sverre’s court about 1200, must have been an exceedingly aged man, if he were still living in 1260. Heffermehl is, therefore, compelled to force the date of composition back to the decade 1230-1240.