Pseudo-Isidorian Decretals around 850: about a hundred forged papal letters, part of canon law for centuries

Around 850 an unknown cleric in the Frankish empire, using the name Isidore Mercator, compiled a collection of canon law into which he inserted about a hundred forged letters of early popes. The forgeries were meant above all to protect bishops from accusation and deposition and to secure church property against secular power, and they made the papacy the keystone of church order. Pope Nicholas I declared all papal letters equally binding, and the texts passed into the Decretum of Gratian. Even the official edition of the Corpus Juris Canonici of 1580 upheld their genuineness; only in 1628 (1620 according to the Britannica) did Blondel definitively prove the forgery.

Period

847-1628 (781 years)

Country

France, Italy

Institutions

Forger in the Frankish empire (pseudonym Isidore Mercator)
Pope Nicholas I
Decretum of Gratian
Corpus Juris Canonici

Category

Forgery

Level of evidence

B two independent scholarly sources · what does this mean?

Persons

Nicholas I (pope 858 to 867, declared all papal letters equally binding)

Background

Course of events

1. The collection was compiled after 847 and before 852, that is around 850, in the Frankish empire. Its author called himself Isidore Mercator, thereby passing himself off as Isidore of Seville. Its origin in the Frankish empire is undisputed today; the ecclesiastical provinces of Mainz, Reims or Tours are discussed.
   Evidence: Encyclopædia Britannica, 11. Auflage (1911), Artikel Decretals, Abschnitt False Decretals

   „The composition of the collection must then be dated approximately at 850.“

   Evidence: Encyclopædia Britannica, 11. Auflage (1911), Artikel Decretals, Abschnitt False Decretals

   „The author assumes the name of Isidore, evidently the archbishop of Seville“

   Evidence: Encyclopædia Britannica, 11. Auflage (1911), Artikel Decretals, Abschnitt False Decretals

   „Everybody is agreed in placing the origin of the False Decretals within the Frankish empire.“

2. According to the Catholic Encyclopedia, about a hundred such documents appeared suddenly in the 9th century without ever having been mentioned before. In the first part, 58 of sixty letters of the popes from Clement to Miltiades are forgeries, and in the third part about thirty more. The Britannica counts differently: seventy fabricated letters in the first part, and in the third thirty fabricated and thirty-five mixed in. The forgeries were skilfully assembled from genuine passages; the authentic elements served as a passport for the forged ones.
   Evidence: The Catholic Encyclopedia, Bd. 5 (1909), Artikel False Decretals

   „These documents, to the number of about one hundred, appeared suddenly in the ninth century and are nowhere mentioned before that time.“

   Evidence: The Catholic Encyclopedia, Bd. 5 (1909), Artikel False Decretals

   „Of these sixty letters fifty-eight are forgeries“

   Evidence: The Catholic Encyclopedia, Bd. 5 (1909), Artikel False Decretals

   „Of these about thirty letters are forgeries, while all the others are authentic.“

   Evidence: Encyclopædia Britannica, 11. Auflage (1911), Artikel Decretals, Abschnitt False Decretals

   „seventy letters attributed to the popes of the first three centuries“

   Evidence: Encyclopædia Britannica, 11. Auflage (1911), Artikel Decretals, Abschnitt False Decretals

   „Thus the authentic elements were calculated to serve as a passport for the forgeries, which were, moreover, quite skilfully composed.“

Why? Justification and motives (according to the sources)

1. According to the Britannica, the forgeries revolve around accusations against bishops: the forger wanted to prevent bishops from being accused, deposed or deprived of their sees, secured for them the right of appeal to the pope, and sought to protect the property as well as the persons of the clergy against encroachments by the temporal power. As the keystone he placed the papacy.
   Evidence: Encyclopædia Britannica, 11. Auflage (1911), Artikel Decretals, Abschnitt Aim of the author

   „his wish is to prevent them from being unjustly accused, deposed or deprived of their sees; to this end he multiplies the safeguards of procedure, and secures the right of appeal to the pope“

   Evidence: Encyclopædia Britannica, 11. Auflage (1911), Artikel Decretals, Abschnitt Aim of the author

   „His object, too, was to protect the property, as well as the persons, of the clergy against the encroachments of the temporal power.“

   Evidence: Encyclopædia Britannica, 11. Auflage (1911), Artikel Decretals, Abschnitt Aim of the author

   „finally, as the keystone of the arch he places the papacy“

Response of the Church

1. The collection passed from hand to hand without meeting any opposition. When it was asked whether decretals outside the recognised collection had the force of law, Pope Nicholas I answered that all papal letters had the same authority; from then on they were accepted and passed into the later canonical collections. Bishop Rothad of Soissons brought extracts to Rome in 864. The Catholic Encyclopedia admits that the popes benefited by the forgeries.
   Evidence: Encyclopædia Britannica, 11. Auflage (1911), Artikel Decretals, Abschnitt False Decretals

   „In fact, the collection thus blended was passed from hand to hand without meeting with any opposition.“

   Evidence: Encyclopædia Britannica, 11. Auflage (1911), Artikel Decretals, Abschnitt False Decretals

   „but Pope Nicholas having answered that all the pontifical letters had the same authority (see Decr. Gra. Dist. xix. c. 1), they were henceforward accepted, and passed in turn into the later canonical collections“

   Evidence: Encyclopædia Britannica, 11. Auflage (1911), Artikel Decretals, Abschnitt Canonical influence

   „It is certain that in 864 Rothad of Soissons took with him“

   Evidence: The Catholic Encyclopedia, Bd. 5 (1909), Artikel False Decretals, Abschnitt Influence

   „it must be admitted that the popes benefited by the forgeries“

2. According to the Catholic Encyclopedia, the Middle Ages were deceived by this huge forgery; many fragments are found in the Decretum of Gratian, the foundational book of canon law. In the 15th century the cardinals Nicholas of Cusa and Juan de Torquemada declared early pieces to be forgeries. Nevertheless the official edition of the Corpus Juris Canonici of 1580 upheld their genuineness.
   Evidence: The Catholic Encyclopedia, Bd. 5 (1909), Artikel False Decretals

   „The Middle Ages were deceived by this huge forgery“

   Evidence: The Catholic Encyclopedia, Bd. 5 (1909), Artikel False Decretals

   „Nevertheless the official edition of the "Corpus Juris", in 1580, upheld the genuineness of the false decretals, many fragments of which are to be found in the "Decretum" of Gratian.“

   Evidence: Encyclopædia Britannica, 11. Auflage (1911), Artikel Decretals, Abschnitt False Decretals

   „No doubts found an expression until the 15th century, when Cardinal Nicholas of Cusa (d. 1464) and Juan Torquemada (d. 1468) freely expressed their suspicions.“

3. The definitive proof was provided by the Protestant minister David Blondel, in 1628 according to the Catholic Encyclopedia, in Geneva in 1620 according to the Britannica. Since then the forgery has been an established historical fact. The last undetected false decretals were pointed out in the 18th century by the Ballerini brothers, two Catholic priests.
   Evidence: The Catholic Encyclopedia, Bd. 5 (1909), Artikel False Decretals

   „In 1628 the Protestant Blondel published his decisive study“

   Evidence: Encyclopædia Britannica, 11. Auflage (1911), Artikel Decretals, Abschnitt False Decretals

   „Pseudo-Isidorus et Turrianus rapulantes , Geneva, 1620“

   Evidence: The Catholic Encyclopedia, Bd. 5 (1909), Artikel False Decretals

   „Since then the apocryphal nature of the decretals of Isidore has been an established historical fact.“

   Evidence: The Catholic Encyclopedia, Bd. 5 (1909), Artikel False Decretals

   „The last of the false decretals that had escaped the keen criticism of Blondel were pointed out by two Catholic priests , the brothers Ballerini , in the eighteenth century.“

See also

• 750-1440 · 690 years

  Donation of Constantine, a forged charter on papal rights of rule

  • France
  • Italy
  • Vatican City
  • Forgery

Scholarly literature and reference works

1. Reference work
   The Catholic Encyclopedia, Bd. 5 (1909): False Decretals, 1 January 1909. Original · Archive copy (retrieved 23 Oct 2026)
2. Reference work
   Encyclopædia Britannica, 11. Auflage (1911): Decretals, 1 January 1911. Original · Archive copy (retrieved 23 Oct 2026)

Last changed on 23 October 2026. Is something missing or wrong? Suggest an addition or correction.