Fort Casimir
United States · built 1651
Fort Casimir was a Dutch fort in the seventeenth-century colony of New Netherland. It was located on a no-longer existing barrier island at the end of Chestnut Street in what is now New Castle, Delaware. It was briefly known as Fort Trinity when in possession of forces from New Sweden.
Fort data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).