The 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 was one of the largest citadels in Europe. Extensively rebuilt by Luca Beltrami in 1891–1905, it now houses several of the city's museums and art collections. The original construction was ordered by local lord Galeazzo II Visconti in 1358–c. 1370; this castle was known as Castello di Porta Giova, from the name of a gate in walls located nearby. His successors enlarged it, until it became a square-plan castle with 200 m-long sides, four towers at the corners and up to 7 m-thick walls.