As head of the Alemannic Institute, the Baden Historical Commission, and Western Studies, he briefly played an influential role in the South-West German scientific organization in the 1930s.
As a prominent figure in medieval studies, he sought to contribute to the intellectual mobilization and demonstrate the relevance of historical research for the nascent European order.
From 1942, he served as president of the Reich Institute for Older German History (formerly known as Monumenta Germaniae Historica), thus holding the highest office in German-language medieval studies.
This also brought Mayer, who had developed an interest in mathematics during his grammar school years, into contact with Alfons Dopsch, a regular guest at the Fickers' house in the summer of 1899.
Like his friend Heinrich Ficker, who subsequently became a meteorologist and climatologist, he became a member of the Academic Alpine Club during his high school years and undertook numerous mountain tours.
[9] He found an advocate for his appointment in his university friend Hans Hirsch, the sole representative of the subject of medieval history and historical auxiliary sciences.
[13] He pursued similar lines of inquiry to his predecessor Aubin, investigating German colonization of the East[14] and continuing to explore topics from his time in Prague.
[24] According to Reto Heinzel, Mayer did not change his political stance abruptly in the first months of the National Socialist government, but continuously, and not for career reasons, but out of inner conviction.
In a letter to Wilhelm Bauer dated 14 March 1938, Mayer, who was oriented towards Greater Germany, commented on the long-awaited "Annexation of Austria" with a mixture of joy and malice towards the fate of the Jewish teachers at Vienna University.
At the end of May 1935, the Karlsruhe cultural bureaucracy appointed Mayer chairman of the Baden Historical Commission, which had been dissolved in 1933 and re-established in 1935 according to the Führerprinzip, not only because of his reputation as a scholar but also because of his political reliability.
[45] He held the rectorate from late autumn 1939 until December 1942, making himself available for a position at the height of the National Socialist rise to power, which not only had to organize the academic world, but also fulfil political functions.
This was a major project of humanities scholars organized by Kiel's Rector Paul Ritterbusch on behalf of the Reich Ministry of Science, Education, and Cultural Affairs, with the goal of creating a European view of history shaped by German historians.
Mayer saw the lenient sentence, which was typical of the time, as a "brilliant justification of my strictly objective, scientific attitude during the entire period of National Socialist rule".
[63] Only in private conversations and letters did Mayer express his criticism of Konrad Adenauer's domestic and foreign policies, "football nationalism," and the danger of black supremacy over the white race.
When he learned that the author of an essay on the Thanner Steinmetz Order was the former Social Democratic Minister of Labor Rudolf Wissell, "the amateurish treatment of the material and the immense breadth seemed clear and understandable" to him.
[115] In the fall of 1941, a series of discussions on the topic of "Questions of German kingship, the high nobility and the peasantry and their significance for the formation of the state from various perspectives" took place in Weimar.
As president, he wanted to integrate the MGH more strongly into historical research beyond its source-related tasks and transform it into a far-reaching institute for the history of the Middle Ages.
According to Jürgen Klöckler, Mayer thus prevented a far-reaching theft of archives, namely the large-scale transportation of deeds, documents, and files relating to Germany to the Reich.
Thanks to this decision, he was able to institutionally anchor young historians in Rome in an expanded art protection department of the military administration, thus sparing them conscription into the German Armed Forces.
In November 1957, Mayer asserted to Eugen Ewig, a prominent figure in the establishment of the Centre Allemand de Recherche Historique, that he was the intellectual originator of the institution.
Besides Mayer, the founding members included the medievalists Karl Bosl, Walter Schlesinger, Helmut Beumann, Heinrich Büttner, Eugen Ewig, Otto Feger, and Franz Steinbach, as well as the Munich Byzantinist Hans-Georg Beck.
[160] Along with Otto Brunner, Adolf Waas and Walter Schlesinger, Theodor Mayer was one of the most important representatives of the so-called "modern German Constitutional History".
The Zähringers established a territory early on through the clearing activities of the abbeys of St. George, St. Peter, and St. Blaise, which they governed, and through towns such as Freiburg and Villingen, which they founded on important roads.
[172] The Nazi newspaper Volksgemeinschaft praised Mayer's explanations in a review: "With reference to our time, it is very instructive that here a modern state essentially expands its sphere of power by reclaiming new land, by reclamation and settlement.
According to this theory, the free peasants of the High Middle Ages in southwestern Germany were not common freemen, but new settlers established by the Hohenstaufen rulers.
The conquest of Gaul by the Merovingian kings was not carried out by free warrior-farmers, but by unfree soldiers, who acquired freedom only through military service and settlement on royal land.
He argued that Theodor Mayer's approach was "just as teleological as that of Swiss research: namely with regard to the history of the German Empire, which was consolidated only very late and which, as a romantic idea, moved people's minds for centuries.
[202] According to Wilfried Hartmann, the error of the older research lies in the fact that far-reaching constitutional-historical conclusions were derived from isolated details in a sparse tradition of sources.
Fried explained that Mayer had avoided the pressing questions, "both about the political failure of historical scholarship in the Third Reich, which he himself had represented in a prominent position, and about the culpability of institutionalized research in general.
[209] The section "German Historians under National Socialism" received the most attention in a discussion on 10 September 1998, led by Otto Gerhard Oexle and Winfried Schulze.