Cronk Howe Mooar is a motte and bailey castle from the late 11th or early 12th century. Steep sided, flat topped and grass covered, 30 to 35 feet high, diameter about 140 feet, surrounded by a well marked ditch which, on the east, cuts across a low spur projecting in that direction. There are faint traces of earthbanks in the wet ground east of the mound.
The famous Italian Medici family have given two queens to France: Catherine, the spouse of Henry II, and Marie, widow of Henry IV, who built the current Luxembourg palace. Maria di Medici had never been happy at the Louvre, still semi-medieval, where the fickle king, did not hesitate to receive his mistresses. The death of Henry IV, assassinated in 1610, left the way open for Marie's project. When she became regent, she was able to give special attention to the construction of an imposing modern residence that would be reminiscent of the Palazzo Pitti and the Boboli Gardens in Florence, where she grew up. The development of the 25-hectare park, which was to serve as a jewel-case for the palace, began immediately.
The architect, Salomon de Brosse, began the work in 1615. Only 16 years later was the palace was completed. Palace of Luxembourg affords a transition between the Renaissance and the Classical period.
In 1750, the Director of the King's Buildings installed in the wing the first public art-gallery in France, in which French and foreign canvases of the royal collections are shown. The Count of Provence and future Louis XVIII, who was living in Petit Luxembourg, had this gallery closed in 1780: leaving to emigrate, he fled from the palace in June 1791.
During the French Revolution the palace was first abandoned and then moved as a national prison. After that it was the seat of the French Directory, and in 1799, the home of the Sénat conservateur and the first residence of Napoleon Bonaparte, as First Consul of the French Republic. The old apartments of Maria di Medici were altered. The floor, which the 80 senators only occupied in 1804, was built in the middle of the present Conference Hall.
Beginning in 1835 the architect Alphonse de Gisors added a new garden wing parallel to the old corps de logis, replicating the look of the original 17th-century facade so precisely that it is difficult to distinguish at first glance the old from the new. The new senate chamber was located in what would have been the courtyard area in-between.
The new wing included a library (bibliothèque) with a cycle of paintings (1845–1847) by Eugène Delacroix. In the 1850s, at the request of Emperor Napoleon III, Gisors created the highly decorated Salle des Conférences, which influenced the nature of subsequent official interiors of the Second Empire, including those of the Palais Garnier.
During the German occupation of Paris (1940–1944), Hermann Göring took over the palace as the headquarters of the Luftwaffe in France, taking for himself a sumptuous suite of rooms to accommodate his visits to the French capital. Since 1958 the Luxembourg palace has been the seat of the French Senate of the Fifth Republic.