In 1977 Menso Folkerts began a project at the University of Oldenburg, supported by a grant from the Volkswagen Foundation, with the title “Materials for the History of Western European Mathematics in the Middle Ages and Renaissance”. The Foundation financed this project for a period of six years, up to 1980 in Oldenburg, and then in Munich. The objective was to gather in a single place descriptions – and, if possible, copies – of all mathematical texts written in Western European languages (Latin and vernacular) between 500 and 1500. For practical reasons the word “mathematics” was used at that time in a relatively strict sense that excluded all texts which, according to modern criteria, belong to astronomy, physics, philosophy or other disciplines. Also excluded were texts written in Greek, Arabic or Hebrew.

The main source for locating these texts were the manuscript catalogues of the different libraries and collections. Everyone working with manuscript sources knows about the difficulties stemming from inadequate printed catalogues, in particular those of the most important manuscript collections. To solve this problem at least partially, Folkerts visited more than a hundred libraries and checked the hand- or typewritten inventories. In total, more than 1300 books, articles, pamphlets and card indexes were consulted, describing about half a million manuscripts, about 150 000 of which are from the Middle Ages. Altogether 2300 of those contain “mathematical” texts in the restricted meaning of the word; some of them contain up to 30 works, while others have only short mathematical notes. Additional information was obtained partly from articles and books on history of science – especially from periodicals such as Zeitschrift für Mathematik und Physik, Abhandlungen zur Geschichte der Mathematik, Bibliotheca Mathematica, Bullettino Boncompagni, Isis, Osiris – and partly by using unpublished catalogues by historians of science describing sources all over the world (A. A. Björnbo, D. W. Singer, M. Clagett) or special collections (M. S. Mahoney: Munich, B. Hughes: Basel). In general, information from these sources is more reliable than that from the library catalogues, because they stem from distinguished historians of science familiar with the contents of the manuscripts.

At the same time as descriptions of manuscripts were collected, copies of these manuscripts were acquired, thus building an archive of mathematical texts in mediaeval Western manuscripts. Most libraries generously provided the project with microfilms or paper copies. The general intention was to order microfilms of the complete manuscript, and accordingly copies not only of mathematical, but also of astronomical and other scientific texts are available in the archive. The collection was enlarged by microfilms donated by the historians of science H. H. L. Busard, P. Kunitzsch and B. Hughes. At present the archive is located in the library of the Monumenta Germaniae Historica in Munich. It contains copies of more than 5000 manuscripts and is an important source for historians of the mathematical sciences of the Middle Ages.

When the grant from the Volkswagen Foundation came to an end, Menso Folkerts obtained another grant from the Deutsche Forschungsgemeinschaft (1985-1989) for establishing a database of mathematical and scientific texts in mediaeval Western manuscripts at the Institute for the History of Science in Munich. At this time, work for compiling a database with the name International Computer Catalogue of Mediaeval Scientific Manuscripts (ICCMSM) started. It was directed in the first years by Warren Van Egmond and later by Andreas Kühne. About ten years later, ICCMSM was renamed to JORDANUS.

The collection of microfilms and paper copies (now at the MGH in Munich) was gradually expanded to about 5000 reproductions, and the cataloguing of the sources was extended in order to include all mediaeval mathematical manuscripts and many related texts as well. Information from different sources was compared and verified as far as possible. The project also collaborated with the Benjamin Data Bank of Mediaeval Scientific Manuscripts, run by N. Hahn in Dunellen, New Jersey.

The database was originally set up at the Lehrstuhl für Geschichte der Naturwissenschaften of the Ludwig-Maximilians-Universität in Munich by Prof. Dr. Warren Van Egmond and Prof. Dr. Andreas Kühne.

The rapid development of computer technology during the 1990s opened up new possibilities for making the database available to a large audience. The wish to make it accessible on the world wide web led to a cooperation between Menso Folkerts for the Institute for the History of Science (IGN) in Munich and Jürgen Renn for the Max-Planck-Institute for the History of Science in Berlin in 1997. In several workshops and working sessions held at the Max-Planck-Institute in Berlin during the years 1998/1999 the raw data were transferred and processed first by Gerd Graßhoff and Michael May, then by Jochen Büttner, Peter Damerow, and Paul Weinig (all MPIWG Berlin).

The most important part of the work was done by Gerhard Brey (IGN, Munich), who checked the more than 60 000 field entries and corrected them whenever necessary with the help of a new interface, Filemaker. An internet-ready version, using MySQL and Perl, was developed and tested in the intranets of both institutions. It was then made available in the world wide web under its new name JORDANUS through the Max-Planck-Institute for History of Science in Berlin, the King’s College in London, and the Institute for History of Science in Munich. After Gerhard Brey’s death (8 February 2012) Jordanus could no longer be maintained on the servers of these institutions. In 2014 Erwin Rauner recovered and reinstalled Jordanus.

In 2017 the hoster ended the support for the implementation used until then. Thus Jordanus was rebuilt within the framework of the project Ptolemaeus Arabus et Latinus at the Bavarian Academy of Sciences in Munich.