[1] Posse made a name for himself in the world of art history by his handling of the museum's collections of German, Dutch and English paintings; a two-volume inventory catalog was published in 1911.
He spent several years in Florence as an assistant at the city's German Institute of Art History, and in Rome as a researcher at the Bibliotheca Hertziana, which resulted in a work on the ceiling paintings of Pietro da Cortona.
Posse reorganized the museum along the new ideas of Bode, and built up its holdings of German paintings, primarily from the 19th century, paying particular attention to the Dresden Romantics.
[1] He was a significant supporter and friend of Oskar Kokoschka, the Austrian expressionist artist, poet and playwright, who was at the time a professor at the Dresden Academy of Fine Arts and become a lodger in Posse's apartment.
After Hitler was appointed Chancellor in January 1933 – the so-called "seizure of power" – the Nazi Party in Dresden launched a smear campaign against Posse, accusing him of displaying "degenerate art" in the museum, and claiming, inaccurately, that he was partly Jewish.
What came to be called the "Führermuseum" – which was never built – was to be the core of a cultural center which was part of a general rebuilding of the city intended to have it surpass Vienna and rival Budapest.
According to Posse's diary, Hitler told him that the museum would contain "only the best of all periods from the prehistoric beginnings of art ... to the nineteenth century and recent time," and the works were to be obtained both by purchase and by confiscation.
[10] Immediately following the Nazi Anschluss with Austria " thousands of paintings were quickly seized following a general ban on Jewish art dealers and gallery owners.
On July 10, 1939, Posse visited the Austrian central depot of artworks confiscated from Jewish art collections, noting in his travel diary "Over 8000 pieces".
These included works by Hans Holbein the Elder, van Dyck, Rembrandt, Frans Hals, Tintoretto, Gerard ter Borch and Francesco Guardi, among others.
He notified me today that there exists at the moment a particularly favorable opportunity to purchase valuable works of art from Dutch dealers and private owners in German currency.
Even though a large number of important works have doubtless been removed recently from Holland, I believe that the trade still contains many objects which are desirable for the Führer's collection, and which may be acquired without foreign exchange.
[8]As a result of this, accounts of about 500,000 Reichsmarks were opened in Paris and Rome for Posse's personal use, and, around July 1940, he expanded the scope of the Sonderauftrag Linz into Belgium and the Netherlands when he established an office in The Hague as Referent für Sonderfragen (Adviser on "Special Questions").
This apparently brought about some internecine squabbling, as Posse had been given the authority to act on Hitler's behalf, and the German commanders of occupied countries were required to keep him regularly informed about their confiscations of artwork.
Probably because of the interference of Hermann Göring – who was busy using the ERR to confiscate art for himself – Posse formally requested that the Reich Chancellery reiterate his power to act for the Führer.
[8] S.A. Gruppenführer Prince Philipp of Hessen was a connoisseur of the arts and architecture and acted as Posse's principal agent in Italy, where he lived with his wife, a daughter of King Victor Emmanuel.
A grandson of the German Emperor Frederick III, and a great-grandson of Queen Victoria, Philipp provided "a veneer of aristocratic elegance which facilitated important purchases from the Italian nobility.
[20] In October 1939, Hitler and Benito Mussolini had made an agreement that any Germanic artworks in public museums in the South Tyrol – a traditionally German-speaking area which had been given to Italy after the First World War in return for entering the war on the side of the Triple Entente – could be removed and returned to Germany, but when Posse attempted to do so, with the assistance of Heinrich Himmler's Ahnenerbe, the Italians managed to keep putting things off, and no repatriations ever took place.