The present appearance of the square is the result of the city planning announced and carried out on the proclamation of Florence as the capital of Italy (1865–71), with particularly intense activity in this Piazza between 1885 and 1895. In this period, known as the Risanamento in the commemorative nineteenth-century terminology (or, by its detractors, the sventramento or ruining), large parts of the city centre were demolished.
The decision to broaden the square allowed the total destruction of buildings of great importance: medieval towers, churches, the corporate seats of the Arti, some palaces of noble families, as well as craftsmen's shops and residences. The demolition was presented as a necessity if the area's insanitary conditions were to be improved, but was in reality led above all to building speculation and to legitimization of the will of the emerging middle-class emergente, protagonist in the events immediately prior to unification.
The porticos with the triumphal arch, called the "Arcone", was designed by a certain Micheli and was inspired by the most courtly Florentine Renaissance architecture, even if its additions to that style seem to be distant from the true ancient style. The pompous inscription that dominates the square was dictated, it seems, from Isidoro del Lungo, or another literary source:
L'ANTICO CENTRO DELLA CITTÀ
DA SECOLARE SQUALLORE
A VITA NUOVA RESTITUITO
(The ancient centre of the city / restored from age-old squalor / to new life)




You might give a look at the gallery in the whole, since all the photos are somehow interconnected...