El Morro, Old San Juan, Puerto Rico
From one fortified town to another, just South of the current French-German border: Wissembourg. In a region rife with conflict, between cities and lords, sometimes between a city and their own lord, protective walls, moats and towers around the town were a must.
This tower, called the Poudrière, was built in the 13th century, and served as gunpowder storage at some point, hence the name. The walls in front of it are more recent, dating back to the 16th century, featuring a dam system which would flood the moat if needed. This complex can be seen in the North-East corner of the town on this 1750 map.
Despite these protections, Wissembourg suffered massively between the 15th and 17th centuries. And in spite of all that, the town centre retains much of its original plan and many traditional buildings. I should go back on a nicer day to get better pictures...
Like other towns on the edge of Louis XIV's Kingdom of France at its peak in the late 17th century, Landau, now in Germany, received the Vauban treatment, transforming the town into an up-to-date garrison and fortress: both the town's ramparts and fort, situated in the North-West corner, were built with in characteristic geometric star shape of the time.
Control of Landau alternated between France and the local lords affiliated with the Holy Roman Empire as battles and sieges between 1702 and 1713 went in favour of one then the other, and remained part of France for another century, as an enclave, until Napoleon's defeat of 1815, when it was handed to the Kingdom of Bavaria.
Today, there is little remaining of the town's ramparts, while some ruins of the fort still stand. Similarly to the Citadelle in Strasbourg, around the walls is a park, while inside is the university and a zoo. Visible in the above shot is a tower built much later than the walls, in 1910, to celebrate Otto von Bismarck - no defensive function whatsoever.