When Duchess Marshal Elżbieta Sieniawska assumes the Wilanów residence, the palace is badly demolished. She employs eminent artists and decides to extend it in line with plans left by King Jan III. Side wings are added to the main body of the palace, thus enclosing the stately courtyard. Elevations and interiors are decorated with splendid paintings and sculptures. The works are supervised by architect Józef Fontana and based on designs by Giovanni Spazzio.