With the Donation of Constantine the corpus of the Pseudo-Isidore is one of the most persuasive forgeries in the history of the West.
A measure of the widespread use of the collections presented can be judged by the fact that seventy-five manuscripts of the Pseudo-Isidorian material have survived, and that they differ widely one from another. Collections of canons were commonly made by adding new matter to old. The forger of the Pseudo-Isidore collection took as the basis of his work a quite genuine collection Hispana Gallica Augustodunensis and interpolated his forgeries among the genuine material that supplied credibility by association.
The official Liber pontificalis was used as a historical guide and furnished some of the subject-matter. The Pseudo-Isidorian collection includes the earlier (non-Pseudo-Isidorian) forgery, the Donation of Constantine. The falsity of the Pseudo-Isidore's fabrications is now admitted; proved by incontestable internal evidence such as the anachronistic use of the language of the Vulgate and of the Breviarium Alaricianum (written in 506) in the decretals of earlier popes. The Pseudo-Isidorian letters were unknown before 852 or 857, the earliest use made of the Pseudo-Isidore material, giving a terminus ante quem.
Immense labor and erudition went into creating this work, and a wide range of genuine sources were employed.
The general agreement is that the work had its origin in the Kingdom of the Franks. The forger's main object was to emancipate bishops, not only from the secular power, but also from the influence of archbishops and synods, partly by exalting the papal power. The uses made of the forgeries form a historical study in themselves.
The work probably had the help of several hands, but was clearly under the editorial control of a very gifted, and for the day, extraordinarily learned man. While an exact identitification is probably impossible, Klaus Zechiel-Eckes has proven that they used manuscripts from the monastic library of Corbie. Zechiel-Eckes has gathered some evidence that an abbot of Corbie monastery, Paschasius Radbertus, (abbot 842-847) might be one of the villains in the piece (K. Zechiel-Eckes, "Auf Pseudoisidors Spur, Forschritt durch Fälschungen?," MGH Studien und Texte 31, 2002, p. 1ff). However, it appears safe to assume that the complex as a whole was more or less completed by 847-852, and that the forgers worked in the ecclesiastical province of Reims. It is possible that its composer was ordained illegally by Ebbo, archbishop of Rheims, during his brief, but unlawful, reinstatement (840-841).
1. The addition of forged material to an earlier, entirely authentic Spanish collection containing texts from councils and papal letters originating in the 4th through the 8th century — the so-called Hispana Gallica Augustodunensis (the name is derived from a manuscript which was at some time in the French city of Autun, Latin Augustodunum).
2. A collection of falsified legislation of Frankish rulers allegedly from the sixth to the ninth century (Capitularies) — the so-called Capitularia Benedicti Levitae — after the name of the alleged author in the collection's introduction: deacon (Latin levita) Benedictus, as he calls himself. The author falsely states that he has simply completed and updated the well-known collection by abbot Ansegis of Fontanelles (died 833).
3. A brief collection on criminal procedure — the so-called Capitula Angilramni — allegedly handed over by Pope Hadrian I to Bishop Angilram of Metz.
4. An extensive collection of approximately 100 forged papal letters, most of which were allegedly written by the Roman bishops of the first three centuries. In the preface to the collection the author of the collection calls himself bishop Isidorus Mercator (hence the name of the whole complex). Besides the forged letters the collection contains a large amount of genuine (and partly falsified or interpolated) council texts and papal letters from the fourth to the eighth century. The genuine and interpolated material derives predominantly from the Hispana Gallica Augustodunensis. (A still excellent overview is Emil Seckels' article in the Protestantische Realencyclopädie)
Apart from these four main pieces there are other minor forgeries derived from the same workshop:
The false decretals attributed to early martyr-popes declare it forbidden so much as to accuse a bishop of a crime, and that eternal damnation and hell awaits anyone who would dare prosecute a bishop. In case procedures should be undertaken against any bishop despite this general rule: at least 72 witnesses of equal rank are required to convict him (anyone would have been very hard pressed to assemble 72 bishops in the West-Frankish Empire); the accused bishop may choose his judges himself; he is allowed to appeal at any stage of the procedure to the bishop of Rome — and many other details making the procedures practically impossible before they even start.
At the same time there is a pronounced animosity against metropolitans and archbishops. They are suspect by default. They may act outside their own diocese only with the expressed assent of all bishops in their province. Those bishops may at any time call on the Pope of Rome against them. In the ninth century the Pope still exercised nothing like the power he had during the later Middle Ages — to say nothing about his position in today's Catholic Church.
Other parts of the forgeries treat in a conventional manner questions of the orthodox faith, mainly the relations of the three persons in the Holy Trinity. Liturgy and sacraments were other questions that attracted the interest of the Pseudo-Isidorians.
The sheer quantity of material emanating from Pseudo-Isidore's workshop is impressive. The collection of papal letters and council texts alone fills more than 700 narrow-printed pages in the (unfortunately not overly reliable) edition by Paul Hinschius (Decretales Pseudoisidorianae et Capitula Angilramni, Leipzig 1863). The workshop's "achievement" is all the more impressive as the falsifications were by no means freely invented, but rather pieced together mosaic-wise from countless genuine texts. The forgers were very learnéd people. The Bible, Roman Law, Frankish and Visigothic legislation, council text, genuine papal letters, obscure local statutes, theological writings, historical works were the quarry for their works. Hundreds of different sources have already been identified and the results are by no means final. Furthermore the forgers did not simply copy their materials but artistically adapted and readapted them in different contexts. Throughout the forgeries, certain sentences of about ten words appear in no fewer than eight different versions.
For approximately 150 to 200 years the forgeries met with only moderate success. Although a relatively large number of manuscripts dating from the ninth or tenth century is known — altogether about 100 more or less complete manuscripts of the False Decretals dating from the ninth to the 16th century have been preserved — the canonical collections took but little note of the False Decretals until the early 11th century.
During the 11th century the situation changed rapidly, under the impetus of the Gregorian reforms and the Investiture Controversy. Under the impetus of monastic reform movements and the efforts of some Holy Roman Emperors a group of cardinals and a series of successive popes strove to cleanse the Church of abuses and free the papacy from its Imperial patronage, which had recently freed it from the influence of the Roman nobles. The reformers' efforts soon conflicted with temporal power. The bishops of the Holy Roman Empire were crucial to the Emperor's power and were the backbone of his administrative structure. Thus the Emperors were keen to maintain their say on who was promoted bishop and who was not. This intermingling of spiritual and temporal power constituted a deadly sin in most reformers' eyes. After all, already St Peter himself had condemned the magician Simon Magus (the "Simon" of simony) who tried to buy spiritual power.
Given this situation, the alleged letters from some of the most venerable Roman bishops fabricated by the forgers' workshop came as a godsend. The close interaction of bishops and Pope was a welcome proof that the Emperors' practice was in blatant contradiction with the oldest traditions of the Church. Collections of canon law rediscovered the False Decretals — some were largely extracts from the forgeries. The forgers' intentions, however, were turned around. They had used Rome's power to maintain the independence of the bishops; now the texts were being used to bring the bishops under close scrutiny and to make them dependents of the Bishop of Rome.
This tendency continued to prevail until around 1140 the learned canonist Gratian published his Concordia discordantium canonum which increasingly replaced the older collections and was soon regarded as authoritative. Gratian, too, made use of texts from the forgers' arsenal, although for the most part probably in indirect ways. With Gratian's work the immediate influence of the False Decretals had come to an end. As intended, the texts had become an important basis for procedural law. But the outcome was nearly the opposite of what the forgers had intended in the mid-ninth century. The bishops' independence was increasingly restricted by the power of the Church of Rome.
A masterly study of the history and the influence of the Pseudo-Isidorian forgeries is H. Fuhrmann, Einfluß und Verbreitung der pseudoisidorischen Fälschungen, 3 vols, Schriften der Monumenta Germaniae Historica 24, i-iii, 1972-3. See also P. Fournier and G. Le Bras, Histoire des collections canoniques en occident, 2 vols, 1931-2.
During the Middle Ages there was little doubt as far as the genuineness of the alleged papal letters was concerned. This changed during the fifteenth century. Humanist scholars of Latin like Cardinal Nicholas of Cusa noticed bizarre anachronisms. Was it really believable that a martyr-pope such as Clement I had founded the preëminence of certain local churches on the fact that the pagans had their high-priests in the same localities? During the sixteenth century Protestant ecclesiastical historians such as the Centuriatores Magdeburgienses (the Magdeburg Centuriators) criticized the forgeries in a more systematic way, although they did not yet recognize the forgeries as one whole interconnected complex. The final proof was provided by the Calvinist preacher David Blondel, who discovered that the alleged Popes from the first centuries quoted extensively from authors of a much later time. In 1628 he published his findings (Pseudoisidorus et Turrianus vapulantes). Some Catholic theologians first tried to defend the genuineness of at least some of the material, but since the nineteenth century no serious theologian or historian has denied the falsification.
Efforts to publish the forgeries have been anything but successful. The Hispana Gallica Augustodunensis has not yet been printed at all. There are several editions of the Capitularia Benedicti Levitae, but the last one (Monumenta Germaniae Historica, Leges, folio II,2, 1831) is more than 170 years old and from a scholarly point of view is rather a step backwards, compared to the edition by Etienne Baluze published in 1677 (reprint in Mansi's Collection of Council texts vol. 17B, online). A new edition is being prepared by W. Hartmann and G. Schmitz, large parts of which are also accessible online The False Decretals and the Capitula Angilramni were printed twice independently. The edition by Paul Hinschius (1863) has sometimes met with unduly harsh criticism, but his choice of manuscripts to form the basis of the edition was rather unfortunate. Moreover, he printed the genuine and interpolated parts of the collection by simply reprinting older versions of Pseudo-Isidore's genuine sources, thus making this part of his edition unusable for critical purposes: for these parts historians must go back to J. Merlin's edition published in 1525 (based on a single 13th-century manuscript) and reprinted in Migne's Patrologia Latina, vol. 130.
An incomplete overview can be found in Sch. Williams, Codices Pseudo-Isidoriani, A Palaegraphico-Historical Study, Monumenta Iuris Canonici Series C vol. 3, 1973, listing 80 manuscripts.
The manuscript tradition is grouped in at least six or seven classes. Most comprehensive is the one called A1 by Hinschius with Vaticanus latinus Ottobonianus 93 (mid-9th century) as the best representative. Of equal importance is class A/B, best represented by Vaticanus latinus 630 (last quarter of the 9th century, from the Corbie scriptorium), The so-called Cluny version dates back to the mid-9th century as well. The original manuscript of this class was preserved: New Haven, Beinecke Library ms. 442 (written after 858), and Class A2 goes back to the ninth century as well: which manuscript is the better is hard to say. Ivrea Biblioteca Capitolare 83 (9c, Northern Italy) and Rome, Biblioteca Vallicelliana D.38 (9c, ecclesiastical province of Reims) are some of the best manuscripts of this class. Three more versions date from the 11th or 12th century; Hinschius class B (e.g., Boulogne-surhhayMer, Bibliothèque municipale 115/116), Hinschius class C (e.g., Montpellier Bibliothèque de l'École de Médecine H.3) and, finally, a version mixing A2 and the Cluny version (e.g., Paris Bibliothèque nationale lat. 5141).
It is hard to say which manuscript class represents the, so to speak, "genuine" forgery. The fact that A1, A/B, the Cluny version and A2 all date to the ninth century night be an indication that the forgers circulated their work from the very beginning in several different versions. It would have been just like them.