The historic center of Castel Guelfo is enclosed by city walls erected in the 14th century with four round towers in the corners. On the westside of the perimeter stands the Cassero, the defensive tower and at one point only entrance to the center.
The military structure with 14th century square design was modified in the 1500s with the installation of large long-range firearms. In the 18th century, it continued to operate as a robust element of the city’s defenses. Interventions between the 18th and 19th centuries led to the transformation of the Cassero into an elegant city gate and removal of its drawbridge.
The four corner towers are peculiar because of their circular sections and their solidity that is a testament to their original military function. Today the towers are privately owned.
The walls that surround the historic center are still easily visible from all sides. About 5 meters tall and 2.5 meters wide, they formed the defensive system in which every element had a function: the Cassero commanded the towers and the towers controlled the subjacent walls.