From the VI century B.C, in Etruscan age, the centre of the town began to develop itself as a watershed between Arezzo and Cortona. The ancient river Clanis, which at that time crossed the Valdichiana, has been drained by Etruscs and represented an important way of navigation. As Romans arrived, they decided, for the fertility of the land, to use this zone to nourish the community.
The things drastically changed with Imperator Augusto. They needed a solution for the floods of Tiber the overflew Rome and they decided that Clanis river was responsible for a series of affluents that lead to the Roman river. The mouth of the Clanis was closed and the river overflew the Valdichiana that became a marsh. The citizens worried about malaria, caused by stagnant water, went away in the closer villages.
The ancient centre after ages of reconstructions was finally called Castiglione. It was under the marquis Monte Santamaria feud. During the Early Middle Age the little town was submitted by the Arezzo’s diocese.
In the second half of the XII century, born the free municipality but after several fights against the bigger municipalities of the area, and the Arezzo’s defeat in 1289 in Campaldino, Castiglione passed under the Florentine domination. In 1303, thanks to the strategic importance of Castiglione, Siena and Arezzo’s troops guided by Uguccione della Faggiuola, took back the city and changed her name in Castiglion Aretino. After the Bishop of Arezzo Guido Tarlati’s death, there were some uncertainties for the city that became in 1336 a property of Florence, then conquered by Perugia became Castiglion Perugino.
During the second half of 1300 happened different important events for the city: the plague halved the population and they revolted to Perugia’s domination taking refuge from the Papal State, then the city finally became a florentian property and took the name of Castiglion Fiorentino.
The beginning of the XV century was hard because of new pestilences and famine. During the war between Florence and Republic of Siena, Castiglioni changed his status but after little time returned to be a Florentine property again. After Medici’s government, in 1765 there was the Lorena’s one. Pietro Leopoldo decided to fix the marsh land assigning the task to Vittorio Fossombrone. In 1799 French took Tuscany.
From 1800 to 1814 Castiglion Fiorentino was garrisoned by Napoleon’s troops but with the Restoration, Lorena’s came back and ultimate the Valdichiana’s drainage. Saturday 21st June 1849 Garibaldi arrived in the city. The 4.000 men took rest at Parterre (today Piazzale Garibaldi) and after taking fund from the local authorities, they continued their march to Arezzo. The Second War world devastated the country: the historical centre were destroyed by bombardments and lots of civilians died due to that fact. The 19th December 1943 the bombardments were really cruel: 71 civilians, women and children too, passed away. In memory of that episode, the 26th January 2004 the city was awarded silver Medal in Civil Merit.