Portchester Castle built
1100 CE.
Shown on the map at 50.837°, -1.115°.
Portchester Castle is a medieval fortress that was developed within the walls of the Roman Saxon Shore fort of Portus Adurni at Portchester, to the east of Fareham in Hampshire. The keep was probably built in the late 11th century as a baronial castle, before Portchester came under royal control in 1154. The monarchy controlled the castle for several centuries; it was a favoured hunting lodge of King John, and was besieged and captured by the French in 1216 before permanently returning to the English shortly thereafter. With a commanding position at the head of Portsmouth Harbour, Portchester was an important port in the medieval period. The castle saw the embarkation for several campaigns to France led by England's kings. In anticipation of a French invasion during the first quarter of the 14th century, Edward II spent £1,100 repairing and reinforcing Portchester Castle. A plot to overthrow Henry V was discovered and the culprits apprehended at Portchester; this event features in Shakespeare's play Henry V. Later in its history, the castle was used as a prison. Today Portchester Castle is a Scheduled monument, and a Grade I listed building.
Text from the Wikipedia article Portchester Castle, licensed CC BY-SA 4.0.