In 1950, the "Federal Ministry for the Affairs of the Marshall Plan" moves to Haus Carstanjen, 1997.
Since 1996, UN organisations have been using the castle, 2000.

Haus Carstanjen

Headquarters of the Federal Ministry of Marshall Plan Affairs

With the "European Recovery Program" (1948–1952), the US were helping rebuild a Europe devastated by war. The fledgling Federal Republic established a special ministry to handle all matters relating to the Marshall Plan, as the programme was called.

The small castle that the Cologne banker and sugar manufacturer Adolf Carstanjen installed on the site of an old estate until 1907 is one of the most eye-catching sights on the banks of the Rhine. In 1950, the "Federal Ministry of Marshall Plan Affairs" moved into the building, having previously been based at Museum Koenig, among other locations.

The Ministry’s name refers to the European Recovery Program that was devised by US Secretary of State George C. Marshall in 1947 and implemented in the following year. The program helped to rebuild a Europe devastated by war, by providing loans, goods, raw materials and food. Marshall was awarded the 1953 Nobel Peace Prize for the program.

Of the 12.4 billion dollars appropriated by Congress for the Marshall Plan, 1.5 billion went to West Germany. When the Marshall Plan came to an end, the Ministry (which was headed by Franz Blücher at the time) was renamed the "Federal Ministry of Economic Development and Co-operation" – and upon its dissolution in 1969, its name was changed to "Federal Ministry of the Treasury". It subsequently merged with the "Federal Ministry of Finance", which in 1951 moved into a building on Rheindorfer Strasse in the northern section of Bonn.

Since 1996, various UN agencies have occupied the entirety of the office complex. The modern extension behind the castle, which was co-designed by Kanzlerbungalow architect Sep Ruf, dates from the late 1960s.