The former "Marstall" is a three-winged, two-storey neo-renaissance building, which was also built from 1873 to 1878 according to the plans of Carl Heinrich Ferdinand Streichhan and used as a courtyard post office and courier station. After the founding of the state of Thuringia, the building was the seat of the ministries of education and justice, during the Nazi regime the seat and prison of the Gestapo. Today, the archive holdings are from 1920 with a reading room here.
Source and more: de.wikipedia.org/wiki/Hauptstaatsarchiv_Weimar#Bestände_und_Standorte
The Marstall is located next to the Residenzschloss and in the vicinity of the Goethe and Schiller archives. Since the 15th century, there were farm buildings and stables on this square.
In 1816 Duke Carl August commissioned the construction of a three-winged complex. But only his grandson Grand Duke Carl Alexander continued the construction in the style of the Neo-Renaissance until the year 1859. From 1873 to 1878 the complex was completed with the construction of a riding hall.