Tuscany was populated, at least by the 7th century BC, by the Etruscans, a mysterious lot who chose to live on hills -- the better to see the approaching enemy -- in such places as present-day Arezzo, Chiusi, Cortona, Fiesole, and Volterra. Some 500 years later, the Romans came, saw, and conquered; by 241 BC they had built the Aurelia, a road from Rome to Pisa that is still in use today. The crumbling of the Roman Empire and subsequent invasions by marauding Lombards, Byzantines, and Holy Roman Emperors meant centuries of turmoil. By the 12th century city-states were being formed throughout Tuscany in part, perhaps, because it was unclear exactly who was in charge.
The two groups vying for power were the Guelphs and the Ghibellines, champions of the pope and the Holy Roman Emperor, respectively. They jostled for control of individual cities and of the region as a whole. Florence was more or less Guelph, and Siena more often than not Ghibelline. This led to bloody battles, most notably the 1260 battle of Montaperti, in which the Ghibellines roundly defeated the Guelphs.
Eventually -- by the 14th century -- the Guelphs became the dominant force. But this did not mean that the warring Tuscan cities settled down to a period of relative peace and tranquillity. The age in which Dante wrote his Divine Comedy and Giotto and Piero della Francesca created their incomparable frescoes was one of internecine strife. Florence was the power to be reckoned with; it coveted Siena, which it conquered, lost, and reconquered during the 15th and 16th centuries. Finally, in 1555, following in the footsteps of Volterra, Pisa, Prato, and Arezzo, Siena fell for good. They were all united under Florence to form the grand duchy of Tuscany. The only city to escape Florence's dominion was Lucca, which remained fiercely independent until the arrival of Napoléon. Eventually, however, even Florence's influence waned, and the 17th and 18th centuries saw the decline of the entire region as various armies swept across it.