Before 1433, the sons of Giovanni di Bicci , Cosimo and Lorenzo – both known as il Vecchio to distinguish them from their descendants of the same name - extended the “old house” of the family by bringing together under the same roof two properties which they owned on either side.
This mansion on Via Larga had the appearance of a long, narrow building of a still mediaeval character, with a garden enclosed within high walls.
Meanwhile, having returned from exile in 1434 and reinforced his political position, Cosimo took over the patronage of several buildings in the vicinity of Via Larga and the Medici houses, which were particularly striking in terms of their beauty and modernity. The Medici effectively promoted the construction and renovation of the convent complexes of San Lorenzo and San Marco, which were the parishes of the gonfalone and consequently the most important churches.
As the work on these enterprises proceeded, Cosimo also bought a number of properties on Via Larga, including, in 1443, several houses on the corner with Via de’ Gori, where shortly afterwards construction began on the new palazzo, designed and directed by Michelozzo.

About ten years later, Cosimo left the “old house” to the descendants of his younger brother, Lorenzo, who had died in 1440, and moved into the just completed palazzo.