Upnor Castle built
1567 CE.
Shown on the map at 51.407°, 0.527°.
Upnor Castle is an Elizabethan artillery fort located on the west bank of the River Medway in Kent. It is in the village of Upnor, opposite and a short distance downriver from the Chatham Dockyard, at one time a key naval facility. The fort was intended to protect both the dockyard and ships of the Royal Navy anchored in the Medway. It was constructed between 1559 and 1567 on the orders of Elizabeth I, during a period of tension with Spain and other European powers. The castle consists of a two-storeyed main building protected by a curtain wall and towers, with a triangular gun platform projecting into the river. It was garrisoned by about 80 men with a peak armament of around 20 cannon of various calibres. Despite its strategic importance, the castle and the defences of the Thames and Medway were badly neglected during the 17th century. The Dutch Republic mounted an unexpected naval raid in June 1667, and the Dutch fleet was able to breach the defences, capturing two warships and burning others at anchor in the river at Chatham, in one of the worst defeats suffered by the Royal Navy.
Text from the Wikipedia article Upnor Castle, licensed CC BY-SA 4.0.