The subject of this article is a mystery within the Arabic administration o
f Norman Sicily. In 1149, the diwan al-tahqiq al-ma mur, the chief supervis
ory office of the Arabic administration of the Norman kings, granted five h
ousehold of Muslim villeins and the estate of Rahl al-Wazzan to the Greek m
onastery of San Nicolo di Churchuro, near Palermo. Five years later, at the
request of the monks, the diwan issued what purports to be an exact copy o
f the donation of 1149, which grants the same five households of villeins,
but a completely different estate, Rahl Ibn Sahl. Recent scholarship has de
clared the 'copy' of 1154 to be a forgery, perpetrated within the diwan. By
means of a new, critical edition of the two documents, and of other releva
nt primary sources, the authors conclude that the mystery is the result not
of a conspiracy to defraud the royal diwan, but rather of administrative i
ncompetence. This conclusion is less important for itself than for what it
reveals about the Norman diwan, and the reception of its products by recipi
ents whose native language was not Arabic.