In 1451 Filarete accepted an invitation from Duke Francesco Sforza to move to Milan, where he started a new career as architect and architectural theorist. He stayed in Milan until 1465, his most important work there being the Ospedale Maggiore, commissioned by Sforza in 1456 with the object of uniting the city's many small hospitals into a single complex. Filarete resigned his post as building superintendent in 1465, when only a small part of the project had been completed. His successors, Guiniforte Solari (1429-1481) and later Giovanni Antonio Amadeo, continued the construction but with a partial change of design. Further alterations in the 17th and 18th centuries mean that the only parts of the present building built to Filarete's design are the south cross-shaped hall with its four courts and accompanying façades. However, in his Trattato, Filarete gave detailed information about his project . The Ospedale Maggiore marks a turning-point in 15th-century Lombard architecture for here, for the first time, an architectural vocabulary is used that is influenced by the Florentine Renaissance, for example in the columned arcades of the courts and façades.