The castle that crowns the headland of Monte Orlando is actually two forts built at different times: the upper Angevin tower dates from the 13th century, while the lower Aragonese fortifications were added in the 15th century under Alfonso I of Naples. The complex was repeatedly enlarged and reinforced as Gaeta's strategic importance grew — it commanded the only good harbour between Rome and Naples.
The castle served as a military installation until the late 20th century and is now open to visitors. The views from the ramparts over the bay, the peninsula, and on clear days toward the Pontine Islands are exceptional. Inside, you can trace the layered history of the fortifications, from medieval masonry to Baroque additions.