With the arrival of the status as capital, the accommodation of ministries and other state offices was resolved by choosing already existing buildings: the offices of the old grand ducal administration, or disused convent complexes. The plan for the expansion of the city, entrusted to the architect Giuseppe Poggi, instead envisaged a series of new quarters to be built beyond the line of the walls. To connect them with the old urban fabric, in the part north of the Arno the city walls were to be demolished. In its place were built large tree-lined boulevards interrupted by squares at the major gates, which were spared for their historical and heritage value. The squares around the Porta a San Gallo and Porta alla Croce gates, in particular, were realised based on unifying architectural concepts and borrowing from British town-planning models, giving rise in the first case to a square with a garden in the centre surrounded by porticoes, in the second to a circus.
In the Oltrarno, Poggi envisaged more limited expansion, concentrated mainly in the flat areas outside the gates at San Frediano and San Niccolò. In this part of Florence, the walled circuit was therefore kept almost intact. Here, too, a ring road was built, which took the form of a panoramic avenue winding along the hills behind the city, culminating in a large terrace overlooking Florence – Piazzale Michelangelo – and connected by a system of ramps to the Arno riverfront.
However, Poggi’s plan did not only concern the expansion of the city, but also included important improvements to its infrastructure. These included hydraulic works for the control of minor watercourses, the new water supply system, and the relocation of the public slaughterhouses from San Frediano to an area on the north-western outskirts of the city.
In the area inside the city walls, the progressive increase in population recorded during the first half of the nineteenth century had already prompted construction and filling of some vacant areas. From 1862, the Maglio quarter was built in the area behind San Marco and Santissima Annunziata; from 1864, the Mattonaia quarter took shape, near San Ambrogio, arranged around a large square. These neighbourhoods were largely intended for the bourgeoisie and did not solve the growing shortage of low-cost housing, aggravated by the arrival of the city’s status as capital. Among the measures taken by the municipality was an agreement (1865) with a philanthropic construction company to build blocks of social housing. The first had already been built in 1849, in the Barbano district; nine others were built in various parts of the city, creating large blocks of flats for the working classes, sometimes equipped with some basic facilities.
At the same time, the plan for the inner city (1866) once again provided for the widening of some streets – including Via dell’Oriuolo, Via dei Cerretani, Via Tornabuoni – and above all the redevelopment of the Mercato Vecchio area. Between the 1880s and 1890s, the entire area, made up of a very old and highly stratified building fabric, was destroyed, replacing it with a regular grid of blocks, where large blocks of buildings used for shops, offices and middle-class residences gave the city centre a more modern image.
This idea of modernity was also reflected in the relocation of the food market, located in a large iron and glass structure that replaced an old down-at-heel area near San Lorenzo; and with the opening of the Zecca Vecchia, Serristori and Torrigiani embankments (1870-1872), which gave full substance to an idea linked to the major road routes and concluded the process of opening the city towards the river.