Montevarchi was born as a market town "Mercatale" along the main road which connected Arezzo to Florence. The town developped in the shadow of the castle, originally the property of The Marquis of Pierle and then Count Guidi. Montevarchi passed under the jurisdiction of Florence in 1273. From that moment it became a border stronghold and an important centre for commerce. It became therefore necessary make sure the town was well protected. The Florentine administration built the city walls in 1328. They enclose the city in an oval shape. The walls, which can still be seen today incorporated in private houses, curved towards Arezzo in correspondence with the river Dogana, otherwise they curved towards Florence. The fortification had two doors at the top and the bottom of Via Roma. The doors were Porta Fiorentina ( destroyed in the XX Century) and Porta Aretina. Other five smaller doors, an ante-wall to protect the market area and two towers also existed. The most important of the two towers was Il Cassero which was joined to Porta Fiorentina by a curved wall. This wall was unearthed during recent building work of the square in front of Il Cassero and highlighted with the use of different paving stones.
Il Cassero's function was therefore military and was made up for "... the tower to which the soldiers' guardhouse is attached. The soldiers come down from the tower to rest once their turn of duty is over..." (Conti, 1770).
The changing political and economic climate affected Montevarchi over the following centuries. From a military outpost it became a manufacturing and agricultural centre (The Medici Farm) at the service of the Florentine Government. The walls were protected and kept until the XVIII Century where they fell into disuse as Montevarchi expanded during the years of peace, political stability and plenty. The fortifications lost their importance and some were destroyed while others were incorporated into houses. The lorenese period increased the process of the privatization of buildings which had up to that moment belonged to the Grand Duchy. The historic centre changed and at the end of XVIII century Il Cassero was sold. The new owner did not modifiy Il Cassero's structure.
However, in the second part of the 19th Century the building was bought by the Province of Arezzo and during the first ten years of the Century Il Cassero underwent major building work. It returned to its military origin by becoming a militarry police station.
In 1996 The Provincial Administration of Arezzo conceded the use of the structure to the Town Hall of Montevarchi which decided to restructure it.
Protected by clause 1089 of 1st June 1939, the building underwent a great deal of careful building work. As a result of the building work, today its roof is in good condition and the interior has two floors; the ground floor which looks out onto the square and the second floor which was created from the battlements. Inside the building the ancient countryard was transformed into a stone staircase which connects the two floors.
In order to carry out the building work Montevarchi Town Council, in accordance with art.12 of law n. 537 of 24.12.1993, applied for funds and on 21.08.1996 received them from the Tuscan Regional Government. The project entitled "Building work for the consolidation and salvaging of Il Cassero" was approved. The Town Council of Montevarchi began work on Il Cassero with the objective of transforming it into a museum and archive.