Context:

Damit hatte der 84-jährige Mommsen ein Projekt initiiert, an dem Profanwie Kirchenhistoriker in Deutschland auch noch lange nach seinem Tode arbeiteten und das gute Fortschritte machte: Al s Jülicher, der nach dem Tode Seecks 1921 die alleinige Leitung übernahm, auf Grund seines Augenleidens 1929 von seinen Verpflichtungen entbunden wurde, Ubergab er der Kommission etwa 75000 Zettel, deren Systematisierung allerdings nicht zum Abschluß kam74. Von einer Veröffentlichung des Materials sah man ab, da «weder der Zustand des Manuskripts noch die inzwischen völlig veränderte wissenschaftliche Lage es gestatteten, die Prosopographie zum Druck zubringen75».

Nachdem nur einige Zettelkästen im Zweiten Weltkrieg verloren gegangen waren, wurde 1951 ein Teil der Materialien leihweise dem von A.H.M. Jones, John Morris und H.-I. Marrou in Cambridge und Paris begründeten Unternehmen, das sich zum Ziel gesetzt hatte, eine weltliche und eine kirchliche Prosopographie der Spätantike zu erarbeiten, zur Verfügung gestellt76. Während wir heute aus technischen und organisatorischen Gründen mit zweiverschiedenen Prosopographien -einer weltlichen und einer kirchlichen- zu arbeiten haben, die beide noch nicht abgeschlossen sind, hatte Mommsen die Nützlichkeit, ja die Notwendigkeit einer spätantiken Prosopographie erkannt, die weltliche und kirchliche Würdenträger gemeinsam erschließt und aufführt.

1. Ibid.: Schreiben H. LlETZMANNs vom 6.10.1936.
2. Weder die Prosopography oflhe Later Roman Empire (= PLRE) noch die Prosopographie chretienne du Bas-Empire erwähnen diesen Sachverhalt; während in PLRE I (hrsg. v. A.H.M. JONES, J.R. MARTINDALE, J. MORRIS), Cambridge 1971, V zu lesen ist: «The project of a prosopographical dictionary of the Later Roman Empire was originated by Theodor Mommsen but... it failed of fruition, largely through the Intervention of the two World Wars. The bulky archives representing the work of many German seholars lay in Berlin during the second war when they were damaged and in part destroyed, together with essential records, during an Allied bombing raid. Consequently when the prqject was taken up in England after the war, the work had to be restarted from the very beginning. The present volume therefore represents the first stage of fulfilment of Mommsen's original project», heißt es im ersten Band der Prosopographie chretienne: A. MANDOUZE (Hrsg.), Prosopographie de l'Afrique chretienne (303-533), Paris 1982, 7: «On sait qu'ä la fin du siecle dernier, sur l'initiative de Th. Mommsen et d'Ad. Harnack, l'Academie des Sciences de Berlin avait commence' ä preparer un vaste dictionnaire prosopographique du Bas-Empire. Sans doute concu de facon trop ambitieuse, victime aussi des sequelles de la Premiere Guerre mondiale, ce projet fut definitivement abandonne" en 1933»; cf. hierzu auch H. CHANTRAINE, Ein neues Hilfsmittel zur Erforschung der Spätantike: Die Prosopographie chretienne du Bas-Empire, in: Francia 11, 1984,697ff., v.a. 697f.

Machine translation:

The 84-year-old Mommsen had thus initiated a project on which both profane and church historians in Germany continued to work long after his death and which made good progress: Al s Jülicher, who took over the sole management after Seeck's death in 1921 due to his eye problems in 1929 was relieved of his obligations, he handed over around 75,000 slips of paper to the Commission, the systematisation of which, however, was not completed ^74. The material was not published because "neither the condition of the manuscript nor the scientific situation, which had meanwhile completely changed, allowed the prosopography to be printed^75".

After only a few card boxes had been lost in World War II, some of the materials were loaned to A.H.M. Jones, John Morris and H.-I. Marrou in Cambridge and Paris, which had set itself the goal of developing a secular and an ecclesiastical prosopography of late antiquity. While today, for technical and organizational reasons, we have to work with two different prosopographies - one secular and one ecclesiastical - both of which have not yet been completed, Mommsen recognized the usefulness, indeed the necessity, of a late antique prosopography that explores secular and ecclesiastical dignitaries together and performs.

1. Ibid.: Letter from H. LlETZMANN dated October 6, 1936.
2. Neither the Prosopography oflhe Later Roman Empire (= PLRE) nor the Prosopographie chretienne du Bas-Empire mention this fact; while in PLRE I (ed. by A.H.M. JONES, J.R. MARTINDALE, J. MORRIS), Cambridge 1971, V one can read: «The project of a prosopographical dictionary of the Later Roman Empire was originated by Theodor Mommsen but... it failed of fruition, largely through the Intervention of the two World Wars. The bulky archives representing the work of many German scholars lay in Berlin during the second war when they were damaged and in part destroyed, together with essential records, during an Allied bombing raid. Consequently when the project was taken up in England after the war, the work had to be restarted from the very beginning. The present volume therefore represents the first stage of fulfillment of Mommsen's original project," says the first volume of the Prosopographie chretienne: A. MANDOUZE (ed.), Prosopographie de l'Afrique chretienne (303-533), Paris 1982, 7: "On said qu'a la fin du siecle dernier, sur l'initiative de Th. Mommsen et d'Ad. Harnack, l'Academie des Sciences de Berlin avait commence' a preparer un vaste dictionnaire prosopographique du Bas-Empire. Sans doute concu de facon trop ambitieuse, victime aussi des sequelles de la Premiere Guerre mondiale, ce projet fut definitivement abandonne" en 1933"; cf. on this also H. CHANTRAINE, A new tool for researching the Late antiquity: The prosopography chretienne du Bas-Empire, in: Francia 11, 1984, 697ff., especially 697f.

This would seem to indicate that Theodor Mommsen potentially had a zettelkasten which he was using to compile his work, but there is some ambiguity here that the slips and boxes may have been those of scholars who came after him and were working on his notes and systematizing them for future publication. Perhaps they were Mommsen's and others were arranging them for potential publication as they only had subject heading orderings, which would have been the most likely mode of the day (versus a more Luhmann-artig ordering.)

syndication link: https://forum.zettelkasten.de/discussion/2649/theodor-mommsens-zettelkasten/

Rebenich, Stefan. “Theodor Mommsen and the Relationship of Age History and Patristic (Theodor Mommsen und das Verhältnis von Alter Geschichte und Patristik).” In Patristique et antiquité tardive en Allemagne et en France de 1870 à 1930 : Influences et échanges: Actes du colloque franco-allemand de Chantilly (25-27 octobre 1991), edited by Jacques Fontaine, R. Herzog, and Karla Pollmann, 131–54. Paris: Brepols, 1993. https://archiv.ub.uni-heidelberg.de/propylaeumdok/46/1/Rebenich_Mommsen_1993.pdf.

https://en.wikipedia.org/wiki/History_of_Rome_(Mommsen)

What was Mommsen's historical method?