The Préfecture des Bouches-du-Rhône is a monumental Second Empire building on the Rue Breteuil, a few blocks south of the Canebière. Designed by the architect Auguste Martin and completed in the 1860s, it was commissioned by Charlemagne-Émile de Maupas, Napoleon III's prefect, as a statement of imperial authority. The ornate facade, with its columns and sculpted pediments, is worth a look even if you can't go inside.
Préfecture
Grand Second Empire administrative building on the Canebière