- There were two King Ferdinands of Spain, Ferdinan IV seems most appropriate for the period in which the film will be set (although this probably won't be implicity stated)
- Ponce de León was a Spanish explorer associated with the Fountain of Youth
Some of the filming is to take San Cristobal Castle at Old San Juan. It was built in 1783 and is the largest fortification built by the Spanish in the new World.
There are also these set pictures:
There is also another set picture of Jack Sparrow running around the ramparts of a Spanish Fort but I'll be damned if I can find it again.