During the 14th century, the city of Florence gained both military and political domination over Prato. Florence wanted the Emperor’s Castle to be connected to the city walls (the Florentine Gate) with a corridor or ‘Cassero’ which would allow them free entrance to the city.
This “corridor” is actually a fortified walkway on two levels, which connected the city wall near the Florentine Gate and the interior of the castle through a back door.
It was built as a secure and silent way for the Florentine troops to enter and exit the city without being seen by the Pratese.
Between 1800-1900 a large section of the cassero was demolished to make way for Viale Piave. The restoration, which was finished in 2000, has re-established the course, creating a pedestrian walkway which runs from Via Pomeria to Viale Piave near the castle. The space is used regularly for temporary exhibits.