The Roquefavour Aqueduct in Ventabren, near Aix-en-Provence, was first planned in 1565, but it was not realized until the 19th century. It was designed by Jean François Mayor de Montricher, built between 1841 and 1847, and is the largest stone aqueduct in the world. It took 5,000 labourers, including 300 stone-cutters, and it cost 3,800,000 French francs. It is 83 metres high, 375 metres long, and the foundations are 9 to 10 metres deep.
The aqueduct brings water (Canal de Marseille) from the Durance river to the Palais Longchamp in Marseille, all the way to La Ciotat.
References:The Gravensteen is a castle in Ghent originating from the Middle Ages. The name means 'castle of the counts' in Dutch. Arnulf I (918–965), Count of Flanders, was the first to fortify this place, building a medieval bastion on this high sand dune, naturally protected by the river Leie and its marshy banks. This bastion consisted of a central wooden building and several surrounding buildings, also in wood.
In the early 11th century, the wooden building was replaced by a stone residence, consisting of three large halls that made up three storeys, connected by a stone stairwell. The monumental stone staircase, the light openings, the fireplaces built into the walls and the latrines were signs of considerable luxury and comfort in those days. There was probably also a tower.