Fortifications of Paris in the 19th and 20th centuries

The fortifications of Paris in the 19th and 20th centuries comprise: The Thiers Wall, surrounding the city of Paris, and farther from the city, The detached forts and their complementary fieldworks. They were built in two stages: 1840–1845: the Thiers Wall and the first ring of forts, about five kilometers from the city; 1874–1885: the second ring of forts, about twenty kilometers from the city.