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JOHANNES LEONIS [GIOVANNI DE LEONE], De synodis et ecclesiastica potestate (On Synods and Ecclesiastical Power)

In Latin, decorated manuscript on paper
Central Italy, c. 1560-1570

TM 707

i (paper) + 103 +i (paper) folios on paper (with watermarks similar to Briquet no. 5964, Enclume: Siena, 1535-1543, Lucca, 1534-1543, Rome, 1539-1542, Siena, 1543-1550; Briquet no. 6291, Flèche: Rome, 1561-1562, Ferrara, 1563; Briquet no. 5924, Echelle: Vienna, 1538, Fabriano, 1532; Briquet no. 493, Ancre: Udine, 1524-1530, Arnoldstein, 1529), contemporary foliation in red ink, upper outer rectos, 1-21, 23-104, f. 22 lost, otherwise complete (collation i-ii8 iii8 [-6, f. 22, with loss of text] iv-xiii8), vertical catchwords written in a fainter script in lower inner margins of qq. i-ii, ruled in hard point with full-length vertical bounding lines (justification 180 x 123 mm.), written above top line in a handsome calligraphic Italic hand on twenty-six long lines, red rubrics, paraphs in red or blue, three- to four-line initials in red or blue begin each chapter, five- to seven-line initials in red or blue begin each book, marginal annotations added by scribe in red, contemporary corrections and annotations in brown ink in at least two other hands, streak on f. 8v from stain or offset, no loss of text, foxing on f. 1, slight worming lower margins of ff. 1-11, some darkening and bleeding of ink on ff. 97-104 slightly impairing legibility, with losses of text on ff. 103-104 due to corrosion of the paper, damp-staining along the edges of leaves, otherwise in very fine condition.  CONTEMPORARY VELLUM BINDING, smooth spine, inscription written on outer edge of the text in Roman capitals, “IO LEO ROM DE SYNODIS ET ECC[LESIASTICA] POT[ESTATE] AD EVGENIV[M] P[A]P[AM] III.”  Dimensions 279 x 201 mm.

Written in an elegant calligraphic hand, this volume presents an unedited, rare fifteenth-century treatise defending papal supremacy.  It is known in only seven other copies, all but one in the Vatican Library.  Tarnished by the Western Schism, the papacy fought to hold its ground against a growing reformist movement that sought to give greater power to a council, not an individual.  This sixteenth-century copy in its original binding witnesses a revival of interest in the defense of papal power that coincides with the Council of Trent and the launching of the Counter-Reformation.


1. Evidence of script and watermarks indicates that this book was produced in Central Italy just after the middle of the sixteenth century, c. 1560-1570.  Contemporary annotations attest to the interest of at least one or two early readers.

2. Penciled seller’s inscription on front pastedown.


ff. 1-104, Ad sanctissimum atque beatissimum patrem [inserted: dominum] Eugenium papam quartum fratris Johannis leonis Romani Ordinis predicatorum, De synodis et ecclesiastica potestate, Incipit liber Primus, incipit, “RErum diuinarum omnes admodum tractatores, qui ad ecclesiastice religionis disciplinam elaborarunt … Si quis iudicata recteque disposita semel [reu]oluere et disputare intendit.  Explicit.”

Johannes Leonis wrote his De synodis et ecclesiastica potestate (On Synods and Ecclesiastical Power) in 1437-1438.  There is no modern critical edition.  Seven other manuscript copies are known (see Kaeppeli, 1975, no. 2428), all but one of which are in the Vatican Library (Biblioteca Apostolica Vaticana).  To our knowledge, this text has not been printed.  According to the Schoenberg Database, there have there been no other copies on the market in the last century.

Johannes Leonis (d. 1463) was a Dominican canonist and theologian.  Based in the province of Rome in the late 1430s, he attended he ecumenical Council of Ferrara-Florence (1438-1445), where he supported the pope’s claim to supreme authority over the Church (see below).  Very likely on the strength of his contributions to the council in support of the pope, Pope Eugene IV (sedit 1431-1447) appointed him bishop of Larino in 1440.

Leonis dedicated this seven-book work to Eugene IV, and within it he argued in favor of papal supremacy and against vesting the supreme authority of the Church in an ecumenical council, that is, an assembly formed by ecclesiastical leaders.  A reformist conciliar movement had begun to seek power in response to the Western Schism (1378-1417), in which rival popes in Rome and Avignon battled for authority in the Church.  The Council of Constance (1414-1418) was finally able to end the schism, securing the abdications of the rival papal claimants and overseeing the election of a single new pope, Martin V (sedit 1417-1431).  In the process, however, that council declared that in some circumstances its authority exceeded even that of the pope.

A similar claim would be upheld at the Council of Basel (1431-1449), which marked the height of conciliar power.  To combat the conciliarists at Basel and to assert more power over the proceedings, Eugene IV relocated the council to Ferrara in 1438 (and the council was relocated yet again to Florence in 1439, on account of an outbreak of the plague in Ferrara).  In Synods, Leonis issued a riposte to one of the most popular defenses of the Council of Basel, the 1433-1434 De superioritate inter concilium et papam (On the Superiority between the Council and the Pope) of Jean Mauroux, patriarch of Antioch (ca. 1408-1439).  Practically speaking, Synods is a polemic against the Council of Basel, one that offers a justification for Eugene’s transfer of the council to Ferrara.

Synods is also a historical work.  In contrast with the largely ahistorical arguments of conciliar tracts like Superiority, Leonis framed his argument for papal superiority in Synods within a history of councils that extends from apostolic councils to the Council of Basel and draws on the Bible, patristic texts, and historical works, as well as council canons.  This history occupies the bulk of the treatise (Books 1 to 4), while the final three books define what pertains to papal power.

The practical value of Synods at the time of its composition may account for the four known fifteenth-century copies of this work.  But, the present manuscript included, three sixteenth-century copies of the work survive as well.  Dedicated to the pope and devoted to the defense of his primacy in the Church at a time when this was under threat, Synods would have appealed to popes and the Curia as reading material in the fifteenth century and beyond (hence, perhaps, the preponderance of copies at the Vatican Library).  The present manuscript, copied during or just after the Council of Trent (1545-1563), could well have served the needs of popes coping with an even greater threat to their power in Europe, the Protestant Reformation.


Delacroix-Besnier, Claudine.  Les dominicains et la chrétienté grecque aux xive et xve siècles, Rome, 1997.

Henderson, Duane.  “Historisierung und historische Kritik an kirchliche Rechtstexten in spätmittelalterlicher Traktatliteratur,” in Autorität und Wahrheit: Kirchliche Vorstellungen, Formen und Verfahren (13. – 15. Jahrhundert), ed. Gian Luca Potestà and Elisabeth Müller-Luckner, Munich, 2012, pp. 179-198 [see especially pp. 190-192].

Kaeppeli, Thomas. “Johannis Leonis (Ley) de Roma,” Scriptores ordinis praedicatorum medii aevi, vol. 2, Rome, 1975, pp. 469-470.

Meersseman, Gilles Gérard.  “Les œuvres de Jean Ley O.P. se rapportant au concile de Ferrare-Florence,” Archivum Fratrum Praedicatorum 9 (1939), pp. 76-85.


Van der Essen, Léon.  “The Council of Florence,” The Catholic Encyclopedia, vol. 6, New York, 1909

TM 707