Royal Citadel @ Starforts.com

England's wars with the Dutch (1664-1667) convinced King Charles II (1630-1685) that the port at Plymouth was vital to his nation's security. Work on the Citadel commenced in 1665, atop an earlier fortification: Fisher's Nose Blockhouse, dating around 1500, was incorporated in the Citadel's southeast corner (lower right on the picture above, but I sure can't see it!). Plymouth's Royal Citadel was to be England's most important fortification for over 100 years.

Built with walls topping 70 feet, the Citadel's guns pointed out to sea and back at the city, which had supported the Parliamentarian side in the English Civil War (1641–1651)...Charles II's dad had been beheaded as a result of that conflict, so one imagines the King may have been a mite touchy on the subject. A small harbor was constructed next to the Citadel so that boats could arm and provision the fort while under the cover of its guns: The harbor is currently the home of the Royal Corinthian Yacht Club.

The Royal Citadel was England's first fortification to declare support for William of Orange when he landed with 15,000 Dutch troops in November of 1688, convincing the garrison (and most of the rest of the country) with his immortal words, "the liberties of England and the Protestant religion I will maintain."

The Citadel remains in use by Britain's military, and is open for guided tours from March through September.