Born in the Diocese of Paderborn, between 1338 and 1340; d. at Maastricht, 22 March, 1418, a medieval German historian, best known for his contributions to the history of the Western Schism. He took his surname from the little town of Nieheim (in the Prussian district of Minden). Nothing is known about his family, and but little about his life previous to his entry into the service of the papal Curia. He spent some time in Italy in the study of law, but never obtained the degree of Doctor. Under Urban V (1362-70) he came to Avignon, and obtained in the papal chancery the office of notary (notarius s. palati), to keep which he had to take orders, if he had not already taken them. When Gregory XI returned to Rome (1377) Dietrich accompanied him. Urban VI conferred on him the lucrative and important office of abbreviator et scriptor in the papal chancery (see ABBREVIATORS); this post he retained under succeeding popes. Boniface IX made him Bishop of Verden (July, 1395), but he never obtained possession of this German bishopric; probably, as Eubel suggests (Hierarchia catholica medii ævi, I, 553), because Dietrich did not expedite with due promptness the documents of his nomination. In August, 1399, another Bishop of Verden was nominated, Konrad von Soltau; Dietrich remained as before a papal abbreviator. In his writings Dietrich is silent about this Verden incident; in a manuscript of the archives of St. Peter at Rome Dr. Göller has discovered twenty-six letters of the years 1398-99 which refer to Dietrich; when published they will probably cast more light on this period of his life (cf. Römische Quartalschrift, 1905, 82-83). About Easter, 1401, Dietrich was at Erfurt in Germany, where he matriculated at the university; in 1403 we find him again active at Rome as abbreviator. Towards the end of the fourteenth century Johann Peters of Dordrecht had founded at Rome a hospital for German pilgrims, known as Santa Maria dell' Anima, still in existence and united with the German national church at Rome. Dietrich was an energetic promoter of the new foundation, to such an extent that after Peters he deserves to be considered its chief founder.

Meanwhile the Western Schism, began in 1378, was still dividing the Catholic world. As a member of the papal Curia, Dietrich was thoroughly informed concerning the origin and development of this unhappy division, and was very active in an effort to close the schism. Dissatisfied with the proceedings of the two popes, Gregory XII (1406-15) at Rome, and Benedict XIII (1394-1417) at Avignon, he adhered to the Council of Pisa convoked (1408) by the cardinals. He took no part in the council itself, being then in Germany, but he worked for the party of the council, recognized as legitimate the Pisan pope, Alexander V (1409-160, also his successor, John XXIII (1410-15), and entered their service. During these years his pen was ever active in the interest of ecclesiastical unity. He is certainly the author of the work known as "Nemus Unionis", in which he describes the various ways (viæ) for putting an end to the schism, and gives important letters and acts (the work was finished 25 July, 1408; ed. Schard, Basle, 1566). He also wrote "Die scismate libri tres", his most important work, finished in May, 1410 (ed. Erler, Leipzig, 1890), in which he delineates the origin and the history of the schism up to the coronation of John XXIII; the abundance of its materials makes this work one of the most important authorities for the last stages of the schism. His judgments, however, concerning persons and facts must be taken with caution, Dietrich being strongly partisan. To John XXIII himself he addressed (perhaps in 1410) a letter about the proper administration of his office ("Epistola ad dominum Johannem XXIII transmissa de bono Romani pontificis regimine", ed. Rattinger, in "Historisches Jahrbuch", 1884, 163-78). This was preceded by a letter of admonition to the cardinals who were to elect John XXIII ("Informatio facta cardinalibus in conclavi ante electionem Papæ Johannis XXIII moderni", written in 1410; ed. Erler, "Dietrich von Nieheim", Documents, XXX-XLI). Of other works ascribed to him mention shall be made later.

Towards the end of 1414 was opened the Council of Constance, destined, if not to remedy all the evils of the time, at least to put an end to the schism. From March, 1415, Dietrich was present at Constance and exerted his best efforts for the restoration of ecclesiastical unity. He was dissatisfied with the attitude of John XXIII, and when the latter fled from Constance (20 March, 1415), Dietrich renounced him. Later, in continuation of his aforesaid work on the schism, Dietrich wrote a history of John XXIII to June, 1416 ("Historia de Vitâ Johannis XXIII", first printed at Frankfort, 1620). This work is at the same time a history of the Council of Constance to the middle of 1416; it is to be noted, however, that the author's judgment is seriously affected by his passionate opposition to John XXIII. Another violent lampoon against this pope, the "Invectiva in diffugientem e Constantiensi concilio Johannem XXIII" (ed. von der Hardt, "Const. Conc.", III, XIV, 296-330) is attributed to Dietrich; it is not certain, however, that he is the author of this fierce pamphlet; Finke rejects quite positively the authorship of Dietrich (Römische Quartalschrift für christl. Altertumskunde und für Kirchengesch., 1887, 48 sqq.). During the council Dietrich kept a diary, as he himself mentions in his "Vita Johannis XXIII"; some fragments of it, according to Finke, are still recognizable (op. cit., 1887, 46-58).

Any final judgment on the attitude and influence of Dietrich at Constance must depend on the authorship of three publications often attributed to him, and dealing particularly with the schism and the efforts at reunion. These are: (1) "De necessitate reformationis Ecclesiæ in capite et in membris"; also entitled "Avisamenta pulcherrima de unione et reformatione membrorum et capitis fienda" (written 1414; ed. von der Hardt, in "Constant. Concil.", I, VII, 277-309; the latter part of it ed. by Finke in "Forschungen zur Geschichte der Konstanzer Konzils", Paderborn, 1890, 267-268); (2) "De modis uniendi ac reformandi ecclesiam in concilio universali" (written 1410, ed. von der Hardt, op. cit., I, V, 68-142); (3) "De difficultate reformationis Ecclesiæ in concilio universali" (written August, 1410; ed. von der Hardt, op. cit., I, VI, 255-69). Von der Hardt attributed the treatise "De modis uniendi" to Johannes Gerson, the two others to Pierre d'Ailly, but was of the opinion that perhaps Dietrich von Nieheim might be the author of the "De necessitate reformationis". Schwab has shown (Johannes Gerson, Würzburg, 1858) that neither Gerson nor d'Ailly can be regarded as the author of these works; he ascribed "De modis uniendi" to the Spanish Benedictine abbot and professor at Bologna, Andreas of Randuf. The other two treatises, he believed, were composed by Dietrich von Nieheim. Sägmüller also saw in the aforesaid Abbot Andreas the author of "De modis uniendi" (Historisches Jahrbuch, 1893, 562- 82). Lenz, however, attributes to Dietrich all three works (see below), and his opinion has been accepted by most later historians; Finke, especially, has confirmed it by numerous arguments. Erler, however, to whom we owe a detailed life of Dietrich (see below), does not admit his authorship of the works in question, while Haller agreees with him in respect to the treatise "De modis uniendi". Mulder has examined (1907) fully (see below) the attitude of Dietrich towards the theological theories prevalent at the council and the contemporary plans for extinction of the schism. He concludes that Dietrich certainly wrote the "De necessitate reformationis" but not the other two treatises. In these three works there is developed a detailed programme of ecclesiastical reform: all three popes are to be removed and the election of the new pope is to be committed to a special electoral assembly. The new pope must execute, during the council, the desired reforms in the administration of the Roman Curia, and the particular practical measures are specified. Erler, as has been seen, denies Dietrich's authorship of these treatises, and therefore sees in him only a very clever papal functionary, who had no higher aims than the extinction of the schism and a reform of the papal chancery. Finke on the contrary, accepting the authorship of Dietrich, thinks that with time his views grew broader, and that, in spite of his weakness as an historian, his bold and influential ideas on ecclesiastical reforms made him eventually one of the most important figures of the early fifteenth century. He calls him the greatest publicist of the later Middle Ages.

After the council we find Dietrich at Maastricht, where he possessed a canonicate; there he fell ill, and on 15 March, 1418, made his testament, by which he bequeathed his property on the German side of the Alps to the hospital newly built by him at Hameln, and his Italian possessions to the German hospital of Santa Maria dell' Anima at Rome. He died in the same month, probably, as stated above, 22 March. Besides the works already mentioned Dietrich composed several others, among them an historical work entitled "Privilegia aut jura imperii circa investituras episcopatuum et abbatiarum," etc. (ed. Schard, Sylloge de jurisdictione imp., Basle, 1566, 785-859), chiefly an account of the Holy Roman Empire. Of the "Chronicon" composed by him only fragments are extant, discovered and published by Sauerland (Mitteilungen des Instituts für œsterr. Gesch., 1885, 589-614; also separately at Frankfort, 1885) and by Mulder (see below). A chronicle of the popes, part of the Liber Pontificalis (Vitæ pontificum Romanorum a Nicolao IV usque ad Urbanum V) formerly ascribed to Dietrich, it is now known, was not written by him. Probably, also, he is not the author of a pamphlet against Cardinal Johannes Dominici ("Epistola Luciferi seu Satanæ ad Johannem Dominici, ord. Præd. presb. card. S. Sixti", ed. in "Nemus unionis"). A geographical work entitled "De regionibus orbis et qualitatibus habitantium in eisdem" written in 1407-1408 is lost. In 1411 he composed a treatise against the heresies of Wyclif: "Tractatus contra dampnatos Wiclivitas Pragæ" (ed. Erler in "Zeitschrift für vaterländische Gesch. und Altertumskunde", Münster, 1885, I, 178-98). For the functionaries of the papal chancery he compiled the guide known as "Liber cancellariæ apostolicæ". He also compiled a short guide to the regular praxis of curial administration, "Stilus palatii abbreviatus" (both edited by Erler, "Der Liber cancellariæ apostolicæ vom Jahre 1380 und der Stilus palatii abbreviatus vom Dietrich von Nieheim", Leipzig, 1888).

VON DER HARDT,Magnum et 'cumenicum Constantiense Concilium (6 vols., Helmstadt, 1700); SCHWAB,Johannes Gerson (Würzburg, 1858); SAUERLAND,Das Leben des Dietrich von Nieheim (Göttingen, 1875); IDEM,Anmerkung zu Dietrich von Nieheims Werke de scismate in Historisches Jahrbuch (1886), 59-66; IDEM,Der sogen. Briefwechsel des Trierer Erzbischofs Hillin und Dietrich von Nieheims Chronik in Neues Archiv (1887), 599-601; LENZ,Drei Traktate aus dem Schriftencyclus der Constanzer Concils (Marburg, 1876); KRAUSE,Dietrich von Niem, Konrad von Vechta, Konrad von Soltau, Bischöfe von Verden in Forschungen zur deutschen Gesch., XIX (1879), 592 sqq., XXII (1882), 248 sqq.; HOUBEN,Eine Studie über Theodorich von Nieheim in Der Katholik (1880), I, 62 sqq.;LINDNER,Beiträge zu dem Leben und den Schriften Dietrichs von Niem in Forschungen zur deutsches Gesch., XXI (1881), 67 sqq.; IDEM,Dietrich von Niem in Zeitschrift für allgemeine Gesch. I (1885), 401 sqq., 516 sqq.; FRITZ, Zur Quellencritik der Schriften Dietrichs von Niem (Paderborn, 1886); IDEM,Ist Dietrich v. N. der Verfasser der drei Constanzer Tractate in Zeitschr. für vaterl. Gesch., XLVI, 157 sqq.; ERLER,Dietrich von Nieheim, sein Leben und seine Schriften (Leipzig, 1887); FINKE,Zwei Tagebücher der das Konstanzer Konzil in Römische Quartalschrift für christl. Altertumskunde und für Kirchengesch. (1887), 46 sqq.; IDEM,Zu Dietrich von Niem und Marsilius von Padua, ibid. (1893), 244 sqq.; IDEM,Forschungen und Quellen zur Gesch. des Konstanzer Konzils (Paderborn, 1889), 132 sqq.; SÄGMÜLLER,Der Verfasser des Traktates de modis uniendi vom Jahre 1410 in Historisches Jahrbuch (1893), 562 sqq.; IDEM,Dietrich von Niem und der Liber pontificalis, ibid. (1894), 802 sqq.; IDEM,Über den 5. Traktat des Nemus unionis, ibid. (1904), 531 sqq.; HALLER,Papsttum und Kirchenreform: vier Kapitel zur Gesch. des ausgehenden M. A. (Berlin, 1903), I, 186 sqq., 483 sqq.; SCHMIDLIN,Gesch. der deutschen Nationalkirche in Rom S. Maria dell' Anima (Freiburg, 1906); MULDER,Dietrich von Nieheim zijn oppvating van het Concilie en zijn Kronik (Amsterdam, 1907); POTTHAST,Bibliotheca historica medii ævi (Berlin, 1906), II, 1051 sqq.

J.P. KIRSCH