The building followed the blueprint of Arnolfo di Cambio, although the construction site, opened in 1299, was coordinated by more masters after the death of Arnolfo. The "new palace", that is the new quarters of the Priors of the Arts, which in the XVth century became della Signoria and then from 1540 the ducal residence, was called "old" because in 1565 Cosimo I chose as palace the Palazzo Pitti, property bought by his wife Eleanor of Toledo. From 1865 to 1871, during the period when Florence was the capital of Italy, it was home to the Italian Parliament. Today it is the seat of the Municipality of Florence.
The palace was built over former buildings, medieval and Roman, such as the theater - under its arches there were cavities that were used as prisons. The original nucleus had been completed in 1302, but the final completion of this first phase of construction lasted until 1315.
The oldest part is formed by a large masonry cube, with Pietraforte ashlar, divided into three floors and delimited by a thin frame, on which, under the robust round arches, lays a double row of mullioned gothic marble windows. These date to the end of the XVIIIth century and replaced the primitive ones; the door - window and the small terrace are also more recent. The projecting gallery crowns and defends the building: it includes a covered and an uncovered walkway, protected by sturdy Guelph-type battlements and supported by corbels, connected by arches, each of which was decorated with a carved head of man or animal. Under the little arches are painted and repeated three times the nine polychrome coats of arms of the Florentine Republic; from left: Captain of the People; the Guelph city; Florence and Fiesole; papal coat of arms; Signoria; the Guelph Faction; Ghibelline city; Charles and Robert of Anjou; Louis of Anjou (Saint Louis of Toulouse), the King of Hungary.
Slightly shifted to the right is the very beautiful tower (94 m high) of 1310, which partially rests on the preexisting tower of the Foraboschi. At the top there is a sequence of pointed arches, rectangular mullioned windows and dovetail battlements. The aedicule of the belfry above has round (semicircular) arches set on powerful masonry columns by leafed capitals and is in turn topped by arches and battlements. The watch has a mechanism from 1667 signed by Giorgio Lederle Augusta and it still works. In the bore of the tower is a cell called “the inn” where Cosimo the Elder (1433) and the Dominican friar Girolamo Savonarola (1498) were imprisoned.
The current staircase of the palace was originally a large platform that run also on its left side and enclosed the area (delimited by a parapet said aringhiera, demolished in 1812) in which the Signoria and other authorities appeared during public ceremonies. During the government of the Duke of Athens (1342-43) the railing was equipped with outer doors that worked as additional elements of defense; the first expansion of the perimeter of the building and the surrounding area were defined.
On the Gothic pediment above the main door (1345) the rayed monogram of Christ the King was set around 1528. Then the gonfaloniere Niccolò Capponi suggested the addition of the dedicatory inscription inspired by Savonarola "Iesus Christus rex florentini populi S.P. decreto electus" (Jesus Christ King of the Florentine People, elected by Popular Decree), replaced in 1551 with the current "Rex Regum et Dominus Dominantium" (King of Kings and Lord of Lords). On the left is a bronze plaque commemorating the plebiscite of March 15, 1860 which united Tuscany to Italy. On either side of the door are two marble statues called termini (XVIth century), originally used to support the chain that blocked the entry: the male statue is by Vicenzo de Rossi, while the other is by Baccio Bandinelli.
On the left side, towards north, the later stages of construction of the building are visible: the XIVth century expansion with the gate called Tramontana (facing North); that of 1495 for the construction of the salone dei Cinquecento (Hall of the 500); that of the upper part erected by G.B. Tasso (1549-55) and Buontalenti (1588-96); on via dei Leoni there is a grand rustic ashlar portal with the ducal coat of arms.
The Tramontana (Northern) portal gives access to the Chamber of Arms, reserved only for the exhibitions and open on rare occasions; originally (in 1312) it was the center of the whole transfer of weapons and armed men. It is the only area of the building that preserves its original structure. It has brick vaulted ceilings with rib vaults and Pietraforte pillars. In the 1910 restoration the original plasters were destroyed and the door facing the square (closed since 1380) was reopened.
After a few changes made during the early Renaissance, the renovations and expansions - while leaving the outer walls untouched - conferred to the inside of Palazzo Vecchio the splendor of a European palace thanks to Cosimo I de Medici, who chose it as his residence; the duke took advantage of the design and construction of Giorgio Vasari, according to a unified plan, a synthesis between past and present.
The first courtyard is the old courtyard of the Palazzo dei Priori renovated in 1453 under the direction of Michelozzo, with the works at the colonnade, the construction of an order of mullioned windows and oculi and decoration of façades with engraved bosses and golden lilies, some traces of which are visible after being recovered in the restoration of 1973. Michelozzo changed it radically, but kept the original staircase, which up to the subsequent transformations, remained leaning against the inside wall.
In 1565, on the occasion of the wedding of Prince Francesco de 'Medici, the eldest son of Cosimo I, with Joan of Austria, the loggia of the courtyard was decorated following the project of Vasari as part of a larger celebratory apparatus: vaults, columns and walls were adorned with grotesques, frescoes and golden stuccoes framing views of the city of the Habsburg Empire, made by Bastiano Veronese, Giovanni Lombardi, Cesare Baglioni and Turino Piemontese. On the same occasion, at the center of the courtyard, a fountain by Francesco Tadda and Rafaele Domenico di Polo was erected to substitute the old well. It was designed by Vasari and with the probable collaboration of Ammannati. The Putto with a Dolphin by Andrea del Verrocchio was placed on the porphyry basin, transferred here from the garden of the Medicean Villa at Careggi; the original, substituted by a copy in 1959, was placed along the museum route, in the terrace of Juno.
In the Cortile della Dogana (Courtyard of the Customs) lay the pillars of the hall of the Great Council, which was later known as the Salone dei Cinquecento, based on a project by and under the direction of Simone del Pollaiuolo also known as the Cronaca. In an environment that communicated with the municipal treasury, the great weathervane with the marzocco and the lily of Florence is exhibited. From 1453 it was located on the cusp of the tower; it was replaced in 1981 by a fiberglass copy; on the left wall are three stone coats of arms from the XIVth and XVth centuries, pertaining to the Captains of the people.