Milan's Visconti rulers built a fortified residence near the city's medieval walls in the fourteenth century, but opponents of ducal power damaged it after the dynasty ended. Francesco Sforza, a military commander who became duke in 1450, rebuilt the stronghold as both defensive center and court. Massive walls, corner towers, moats, gates, service quarters, and residential ranges projected the authority of a new ruling family. Florentine architect Filarete designed the principal entrance tower, while later engineers improved fortifications as artillery reshaped warfare.

Under Ludovico Sforza in the late fifteenth century, the castle became a major Renaissance court. Bramante worked on architectural spaces, and Leonardo da Vinci designed decorations, entertainments, engineering schemes, and paintings, including surviving traces in the Sala delle Asse. Diplomats, musicians, artists, soldiers, administrators, servants, and artisans filled the complex. French invasion in 1499 ended independent Sforza rule. An ammunition explosion in 1521 destroyed the Filarete Tower, and successive French, Spanish, and Austrian governments converted the former palace into a garrison and citadel.

Early modern rulers surrounded the castle with star-shaped outer defenses and used its rooms for barracks, stores, prisons, and military administration. The Napoleonic era removed the exterior fortifications, opening surrounding land but leaving the core complex damaged and utilitarian. After Italian unification, some Milanese leaders proposed demolition as an unwanted symbol of foreign domination. Preservation advocates instead reimagined it as a civic monument. Architect Luca Beltrami directed extensive restoration from the 1890s, using documents and comparisons to rebuild missing features and create museum spaces.

Beltrami reconstructed the entrance tower, rooflines, battlements, windows, courtyard features, and interiors, sometimes making interpretive choices where evidence was incomplete. Later bombing in 1943 caused further damage, followed by postwar repair and museum renewal. The castle retains substantial fifteenth- and later masonry, courtyards, and archaeological fabric, but its present unified appearance owes much to late nineteenth- and twentieth-century restoration. Frescoes, ceilings, portals, and sculptures vary in survival, while galleries contain civic collections assembled from many places rather than furnishings continuously preserved in ducal rooms.

The City of Milan operates Sforza Castle as a public complex containing museums, libraries, archives, cultural programs, and open courtyards. Grounds are generally free, while museum collections and exhibitions follow current ticket and access rules. Conservation must balance fragile artworks, dense tourism, events, and a building repeatedly altered for government and war. The castle's history is clearest when its layers remain distinct: Visconti foundations, Sforza court, foreign garrison, demolished bastions, Beltrami's civic reconstruction, wartime repair, and modern museum use. It is neither a pristine Renaissance palace nor merely a Victorian replica.