Over the course of the 14th century, the Florentine government transformed the building into to a military garrison and prison, linking it with the 14th-century city walls by way of a covered walkway: the Cassero.
Inside is a large courtyard and tower rooms. An internal stairwell in the eastern corner leads to the upper walkway that runs along three sides of the building. From here, you can enjoy a magnificent panoramic view of the monuments in Prato and the surrounding hills and plain.
During the summer, the Emperor's Castle also hosts numerous events, concerts and movie projections.