He preferred a Byzantine hybrid style (Military Museum in the Arsenal, 1856, (see) Museum of Military History).
Around 1859 created the "Wiener Stil", a neo-Renaissance style with austere classical aspects, to which he later added monumental total work of art characteristics (Musikverein - building of the Gesellschaft der Musikfreunde in Wien in Vienna, 1870).
His buildings along the Ringstraße, especially the house of Parliament, 1874-1883, and the town palaces with their disciplined magnificence symbolise the climax of the austere architectural style during Viennese Historicism and are a reminder of the leading role Austria played in the field of architecture.
He had a number of great students, even Otto Wagner worked with him. From 1868 at the Academy in Vienna, he emphasised classification according to style.
Other works incl.: Vienna: Protestant church at Matzleinsdorf cemetery, 1858; Protestant School, 1859-1862; Heinrichhof, 1860-1862 (destroyed 1945); Palais Erzherzog Wilhelm (Hoch- und Deutschmeisterpalais, now The OPEC Fund for International Development), 1864-1868; Palais Epstein, 1868-1872 (in co-operation with O. Wagner); Börse (stock exchange in co-operation with C. Tietz), 1870-1877; Academy of Fine Arts, 1871-1876. Lower Austria: Schloß Hernstein, 1856. Athens: Zappeion, 1845; Academy of Sciences, 1856.