Older than Florence itself, Fiesole is the site of the original Etruscan settlement. Florence was actually colonized and settled as an off-shoot. Fiesole has long been a welcome escape from the sweltering summer heat of the Arno Valley and a source of inspiration for numerous famous figures---among them L. Sergius Catilina, Alexander Dumas, Anatole France, Marcel Proust, Gertrude Stein, Frank Lloyd Wright, and Paul Klee. Leonardo da Vinci even used the town as a testing ground for his famed flying machine. Fiesole's location provides incomparable views of Florence and the rolling countryside to the north.

Source: Let's Go Italy

Numerous founds of Etruscan civilization have come to light in the vast zone to the north of the Arno between the Sieve and Ombrone rivers. The so-called "Fiesole stelae" date back as far as the late 6th century B.C. However finds from the Villanovan culture of the early iron age and the age of copper and of bronze have also been unearthed. The Etruscan settlement of Fiesole was probably the center of a zone where settlements were scattered over the hillsides which overlook the Florentine basin. Remains from this period include various stretches of the powerful city wall and the ruins of a Temple with two wings and two columns in the pronaos. Since some of the walls are still intact it can be considered as one of the most important examples of this kind in all of Etruria. A considerable number of interesting finds from the Etruscan period - urns, bucchero, clay and bronze statues - together with other objects from Roman times are to be found in the Museum near the archaeological zone. Invaded by the Gauls in 225 B.C. and captured by Marcus Porcius Cato in 90 B.C., it was occupied by Silla in 80 B.C. and turned into a military colony. This was when Fiesole became a Roman city (Faesulae) with a forum, temples, theater, baths. The Theater, which is still well preserved, is sometimes used for spectacles of classic theater and has a capacity of about 3.000 people. It dates to the beginning of the imperial age and was improved in the period of Claudius and of Septimius Severus. The Baths too belong to the early empire and were remodelled by Hadrian.

In republican times (1st cent. B.C.) the Temple, originally Etruscan was rebuilt. an explanation for the prosperity of Etruscan and Roman Fiesole is to be found in its fortunate geographical site near a ford over the arno - close to where Florentia was to rise. The territory of the Roman Municipium of Fiesole must have extended prevalently to the north of the Arno while the territory of the "colonia" of Florence must have lain above all to the south of the river. Occupied by the Ostrogoths and the Byzantines, Fiesole from the 6th century on was the site of a Lombard settlement as documented by the remains of a necropolis. In 1125, after military compaigns, Florence wiped out the city forcing it into submission and destroyng part of the centuries-old city walls.

Source: Your Way to Florence