The Mainz series of papersThe series of papers now being reprinted as Golden Oldies were the product of Pascual Jordan's strong relativity group at Hamburg University in the immediate postwar period, initially comprising Jordan, Jürgen Ehlers, and Wolfgang Kundt, and later also Rainer Sachs and Manfred Trümper. Jordan made major contributions to quantum mechanics and quantum field theory 1 (Jordan algebras are named after him) before switching attention to gravitation and cosmology, mainly working on variable-G theories and authoring the book Schwerkraft und Weltall [1]. This group interacted strongly with Otto Heckmann and his student Engelbert Schücking at Hamburg Observatory. Heckmann directed Hamburg Observatory from 1941 to 1962, after which he became the first director of ESO (the European Southern Observatory) and won the Bruce Gold Medal. 2 Schücking states 3 "The first edition of Jordan's book came out in 1952 when I began to work with Jordan, and the second edition carries the subtitle 'Zweite erweiterte Auflage Bearbeitet unter Mitwirkung von E. Schücking'. This second edition contains extensive results from my Master's and PhD Theses. I was already working with Jordan when Ehlers and Kundt began to study with him. It was thus natural that Jordan brought us together because he wanted us to work on his theory. I did not believe in Jordan's scalar-tensor theory and Juergen was also not enthusiastic about it. We both felt that Einstein's 1916 theory had not been understood. Since Jordan had no longer time to actively work on his theory (he was a member of Parlament, gave numerous popular science talks and worked on his theory of skew lattices) we subverted his seminar into one on GR."Kundt states 4 "The core of the Hamburg group was Engelbert, Juergen, and me, initiated by Jordan, and mostly attended by Jordan, rarely by Heckmann. Initially, Jordan contributed actively, later hardly. But he also attracted guests like Pauli, Joshua Goldberg, Peter Bergmann". Ehlers helped focus the group's work on the structure and interpretation of Einstein's general theory of relativity. 5 More than that, the focus was on exact solutions (Strenge Lösungen) of the Einstein Field Equations of General Relativity Theory, seeing what could be achieved without approximations: a crucial effort in the case of a theory as non-linear as General Relativity. It resulted in a major series of papers, the so-called Hamburg Bible [5][6][7][8][9], setting out the results of this work. 6 Jordan's name was on the first three of the papers, although he in fact did not take part in writing them: his name was there simply because he was the head of the group from which they came. Schücking played an important part in the seminar discussions, even though his name does not appear as an author in any of this series of papers. 7 Why were they published in the Proceedings of the Akademie der Wissenschaften und der Literatur in Mainz, when the authors were based in Hamburg? Well, Jordan was elected a member of that Academy in 1949, and was its pr...