In 1846, Baron Mayer Carl von Rothschild purchased the house at No. 15 from banker Speyer's widow. In the course of the following years, he had it altered by Friedrich Rumpf, and extended westwards by five windows. Planned as a representative summer residence with park-like grounds, the addition of a second gable finally gave the building its present appearance.
Moreover, Friedrich Rumpf created a new interior with reception rooms in the historicist style that came to be known as “le goût Rothschild”. The stairway with mirrors and coloured marble incrustations in Renaissance style leads down to the reception rooms, of which three salons have survived in their original form. They are the Louis XIV style wood-panelled smoking salon with fluted columns mirrors and gilded coffering on a blue ground.
The adjacent music salon in Louis XV style is decorated entirely in gold and white, with the arrows from the family coat of arms featuring in the gilded boiseries. The little salon in Louis XVI style has plain, pale green wall panels in the emergent neo classical style of the day, while the ornately gilded stucco ceiling still bears all the hallmarks of rococo.