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:Bomarsund fortress and garrison was built in 1832-1854 by Russian Empire to defence Åland Islands against enemies. British and French fleet attacked against it during the Crimean War in 1854. After a week of fighting the British stormed the remaining fort. Anglo-French forces destroyed it totally after battle. In the Treaty of Paris 1856, the entire Åland Islands were demilitarized, which is a status that has been preserved until this day.
Nowadays there are some ruins left and fortress area is open for visitors.