Porchester Castle. Portchester Castle is a medieval castle built within a former Roman fort at Portchester to the east of Fareham in the English county of Hampshire. Probably founded in the late 11th century, Portchester was a baronial castle taken under royal control in 1154. The monarchy controlled the castle for several centuries and it was a favoured hunting lodge of King John. It was besieged and captured by the French in 1216 before permanently returning to English control shortly thereafter. Occupying a commanding position at the head of Portsmouth Harbour, in the medieval period Portchester was an important port. The castle saw the disembarkation 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 E1,100 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 Ancient Monument, and a Grade I listed building. The castle has been in the ownership of the Southwick Estate since the 17th century but is managed by English Heritage and open to visitors throughout the year. The Norman church, St. Mary's, which stands in the south-east corner of the grounds, falls within the Anglican Diocese of Portsmouth. Main article: Portus Adurni The strategic importance of Portchester has been recognised since at least the 3rd century when a Roman fort was established on the site of the later castle. Though it is uncertain exactly when the fort was constructed, it is thought that it was built by Marcus Aurelius Carausius on the instructions of emperor Diocletian between 285 and 290. It was one of several forts built along the British coast in the period to combat raids by pirates. Portchester was probably a base from which the Classis Britannica, the Roman fleet defending Britain, operated. It is the best preserved Roman fort north of the Alps. Although the Roman army retreated from Britain in the early 5th century, it is unlikely that the fort was ever completely abandoned, although its use continued on a much smaller scale. A 10th-century hall and tower were discovered within the fort, suggesting it was a high-status residence during the Saxon period. In 904, Portchester came into the possession of King Edward the Elder and the fort became a burh to help defend the country against Vikings. It is uncertain when the castle was built, although it was probably in the late 11th century. In the aftermath of the Norman Conquest, the manor of Portchester was granted to William Maudit, an associate of William the Conqueror and a powerful magnate, and it was probably he who built Portchester Castle. The form of this early castle is uncertain, although Maudit was probably responsible for creating the inner ward in the north-west corner of the fort. At this point it would probably have been defended by a wooden palisade and a moat, with the original Roman stone walls of the fort acting as the defence of the outer bailey. Maudit died in about 1100, and his property passed onto his son, Robert Maudit. He died in 1120, and a few years later the family estates came into the hands of William Pont de l'Arche through marriage to Robert Maudit's daughter. Although the castle was still unrecorded in this period, it was probably at this point that it was rebuilt in stone. The evidence for this is that the stonework of the castle is similar to that of St Mary's parish church, which was built in the 1130s in the outer bailey. The church was built for an Augustinian priory which Pont de l'Arche established within the castle in 1128. Other buildings would have been planned for the priory, although almost no trace of them survives. As the community moved to a new site at Southwick between 1147 and 1150, the buildings may never have been completed. William Pont de l'Arche probably retained possession of Portchester Castle until his death in 1148, although who inherited it is uncertain. It may have passed to William Maudit, a descendant of the Maudit who most likely founded the castle, or Henry Maudit, William de l'Arche's son. The earliest extant reference to the castle is in a grant from 1153 in which Henry Plantagenet, later King Henry II granted the castle to Henry Maudit. Regardless, when Henry ascended to the throne in 1154 he took over possession of Portchester Castle. It would remain in royal control for several centuries. More records survive from the castle's period as a royal fortress than the previous period; the royal accounts provide details of the castle's condition and structure.