Ancient region of Caiano
Although Poggio a Caiano is a town, the Caiano historically referes to a larger region, as explained by Tigri:
"Caiano, currently restricted only to Poggio a Caiano, was a vast area in ancient times that spread from Ombrone to Cafaggio“ .
The area around Poggio was probably a swampy place, as noted by Livius and also generally accepted by contemporary historians:
"With regard to the Tuscan swamps, according to Polybius (200-118 BC) and Livy (59 BC-17 AD), Walbank himself accepts the opinion of G. de Sanctis, according to whom they would be those between Pistoia and Fiesole" 
In fact it seems certain that at that time the plain between Prato and Poggio a Caiano was occupied only by ponds and by waters of the river Bisenzio. The presence of the Etruscans has also been hypothesized but:
"the Etruscan settlement in the valley of the Ombrone-Bisenzio was generally scattered in this region (...) In the north-west, beyond a line joining Montemurlo with Poggio a Caiano, the Etruscan presence was even more reduced " .
However, some important finds of Etruscan origin were found in the territory, like the Etruscan tombs of Comeana near Poggio.
Medieval Poggio a Caiano
Poggio a Caiano was mentioned in medieval times, when Prato built a bridge on the river Ombrone to join the plains with the hills of Montalbano:
"The bridge of Caiano existed in 1268 when the General Council of the Commune of Prato treated to elect a worker who could attend to the bridge (...) In fact for some time Prato had some rights over that bridge" .
This building was joined to a fortress located on the hill west of the bridge and allied with Prato, which realized the strategic importance of Poggio. The fortress, which passed to the Cancellieri family in 1420, who transformed it into a castle with a park, was sold to the Strozzi family and then passed to the Medici at the end of the 15th century - the Medici kept the property until the early 18th century.
Villa Medici at Poggio a Caiano
The detail of the construction of the villa at Poggio a Caiano is uncertain, but we know that Giuliano da Sangallo (1445-1516) was appointed by Laurence the Magnificent, at the end of 1485, with the intention of creating a hunting lodge. But if Giuliano da Sangallo was appointed to oversee the work, there is reliable evidence that Laurence the Magnificent conceived the essential features of the villa because he was interested in architecture and in particular the work of Leon Battista Alberti (1404-1472).
The work was interrupted and then resumed in 1512 and intensified in 1515. In 1562 Giorgio Vasari (1511-1574) designed the main entrance and presumably the ground floor of the villa, known as "Bianca Cappello". Between 1801 and 1811 Pasquale Poccianti (1774-1858) realized the staircase.
Works on the gardens of Poggio a Caiano were undertaken under Cosimo I (between 1542 and 1552), conducted first by Niccolò Tribolo (1500-1550) and then by Davide Fortini (died 1594). At the death of the last descendant of the Medici family, Poggio a Caiano passed to the Dukes of Lorraine, who had also owned the Villa Medici.
The last 200 years
The Lorena's domination period lasted until the early 19th century, when the territory of Poggio a Caiano was invaded by the French, who settled in the territory until 1814.
In 1815 Poggio a Caiano was annexed to the Grand Duchy of Tuscany and in 1861 it was united to the Reign of Italy by King Vittorio Emanuele II (1820-1878) of Savoy.
Origins of the name Caiano
In the nineteenth century, about the antiquity of the site of Poggio a Caiano, G. Tigri wrote:
"It is said that the name of Villa Poggio a Caiano derives from the name of the Roman family of the ‘Caii’, later called ‘de Caiani’, and "rus Caianum" or ‘Villa Caiana’. To the small island formed near the Ombrone north of the Villa, Laurence the Magnificent (1449-1492) gave the name of “Ambra” .
With regard to the etymology of "Caiano," the hypotheses of G. Tigri have been confirmed, and therefore the name derives from the presence of a "fundus Caiani", that is a plot of land belonging to a Roman owner called "Caius":
"Many are the place names in Tuscany whose origin are attributable to this ancient fiscal and Administrative practice. They are usually well known for their termination 'anus' or 'ana', such as Caiano (from ‘Caius’)" .
"Poggio" (from Latin "podium" [= hillside]) refers to the slight rise on which the town is located. Poggio a Caiano was therefore of Roman origin, as evidenced by the personal name derived from the Latin "Caius", although "Caianum" indicated a wider area than the current small town.
See the visitor guide for Poggio a Caiano.
1. See G. Tigri, “Pistoia e il suo territorio”, 1853, p. 345
2. See F. Braudel, “Prato, storia di una città”, 1997, Vol I, p. 136 notes 82 and 15 and 16
3. See “Storia di Prato”, 1980, Vol I, p. 40 note 2
4. See N. Rauty, “Storia di Pistoia”, 1988, p. 11
5. See “Fiesole, una diocesi nella storia: saggi, contributi, immagini”, 1986, p. 260
6. See “La Villa medicea di Poggio a Caiano”, 1981, Vol I, p. 62