Epistola Adefonsi Hispaniae regis

The Epistola Adefonsi Hispaniae regis anno 906 (“letter of Alfonso, king of Spain in the year 906”) is a letter purportedly written by Alfonso III of Asturias to the clergy of the cathedral of Saint Martin's at Tours in 906. The letter is primarily about the king of Asturias purchasing a crown kept in the treasury of the church of Tours, but it also includes instructions for visiting the shrine of James, son of Zebedee, which lay in Alfonso's kingdom. An exchange of literature was also arranged in the letter. Alfonso requested a written account of the posthumours miracles worked by Saint Martin. In return the church of Tours would receive the Vitas sanctorum patrum Emeritensium, a hagriography of some early Bishops of Mérida.

The authenticity of the letter is widely questioned and "it has generally been regarded with scepticism by modern historical scholarship." It is rejected, for example, by Lucien Barrau-Dihigo, although it has been accepted as genuine by Hermann Hüffer,Carl Erdmann, and Richard Fletcher.

The letter was copied into a cartulary of Tours compiled between 1132 and 1137, but which was destroyed in 1793. A copy was made for the 17th-century antiquary André Duchesne, and this is the copy from which all modern editions derive. Since no earlier copy survives, it is impossible to ascertain at which stage of transmission the corruptions in the present manuscript were introduced. No correspondence of the kings of Asturias, Castile or Kingdom of León has survived from before the 12th century save this letter, if authentic. For all these reasons neither the science of palaeography nor that of diplomatic can solve the problem of authenticity. If a forgery, the letter must pre-date the 1130s, when the cartulary of Tours was compiled.

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