In the 14th century, Prato had a fortified walkway known as the Corridore del Cassero. After the subjugation of Prato to Florence, in 1351 the Florentines built a 230 meter long corridor that directly connected the walls, near Porta Fiorentina, with the interior of the Emperor's Castle through its rear gate. The Keep represented an elevated, safe and silent route, which allowed the Florentine troops to enter and exit the city without being seen by the people of Prato.

A significant part of the Keep was demolished between the 19th and 20th centuries to make room for the current Viale Piave. However, thanks to a careful restoration, in 2000 two sections of the ancient structure were recovered and a pedestrian path was restored which from Via Pomeria reaches Viale Piave, a stone's throw from the Castle. Today, this space is used for events and temporary art exhibitions.

Entering the Keep and climbing the stairs, we find ourselves immersed in a long stone corridor. Along the way, we notice a series of small rectangular windows alternating with lunettes that offer a fascinating view of the city. Reaching the upper part of the Keep, we find ourselves facing a stretch of the external walkway, from which we can admire the grandeur of the ancient castle and enjoy a breathtaking view of the city. From here, the gaze extends far away, allowing us to embrace the entire surrounding landscape.