Sforza Castle was built in the 15th century by Francesco Sforza, Duke of Milan, on the remains of a 14th-century fortification. Later renovated and enlarged, in the 16th and 17th centuries it became one of the most massive citadels in Europe. Extensively rebuilt by Luca Beltrami in 1891–1905, it now houses several of the city's museums and art collections. For centuries the Milanese considered the castle to be an emblem of both tyranny and foreign rule and therefore attempted to assault and demolish the hated fortress on various occasions. Only after the unification of Italy and its conversion to a cultural center the castle truly become dear to the hearts of the Milanese and as such, a symbol of the city.