Flint Castle Flint Castle ( ) located in Flint , Flintshire , was the first of a series of castle s built during King Edward I ' s campaign to conquer Wales . The site was chosen for its strategic position in North East Wales . The castle was only one day ' s march from Chester , supplies could be brought along the River Dee and there was by a ford across to England that could be used at low tide . Construction . Building work began in 1277 under Richard L ' Engenour , who would later become Mayor of Chester in 1304 . The castle and its earthworks were built by 1 , 800 laborers and mason s using local Millstone Grit ashlar and sandstone . In November 1280 , the Savoyard master mason James of Saint George began overseeing construction at Flint for Edward I . He remained at the castle for 17 months . James of Saint George then moved onto Rhuddlan to oversee its completion . When work ceased in 1286 , Flint Castle had an inner ward and an outer bailey . They were separated by a tidal moat and were connected with gatehouse and drawbridge . A plantation town was also laid out beyond the outer bailey . The inner ward had three large towers and a detached keep . This isolated tower protected the inner gatehouse and outer bailey . In total expenditure , Edward I spent £6068 . 7 . 5d . creating the fortress and the town ( £ as of 2008 ) . Flint , which was sited on the western shore of the River Dee estuary , could be supplied by river or sea . Its harbour was protected by a defensive wall . The castle lies opposite to the English shore and Shotwick Castle in England . Before the river ' s course was drastically changed in the 18th century , passage across the estuary at this point could be made directly by boat at high tide or by fording at low tide . Unique fortress design . The castle is based on medieval French or Savoyard models where one of the corner towers is enlarged and isolated . This independent structure served as both corner tower and keep or donjon , like at Dourdan , France . Flint ' s keep has been compared to the donjon at Aigues - Mortes , France . Edward I would have been familiar with Aigues - Mortes having passed through the fortress on the way to join the Eighth Crusade in 1270 . The keep is an impressive structure . Its stone walls are thick at the base and above . Access was gained by crossing a drawbridge into a central entrance chamber on the first floor . Originally there would have been at least one additional storey . These floors had small rooms built into the thick walls . A timber gallery was built on top of the keep for the visit of Edward , Prince of Wales in 1301 . On the ground floor is a vaulted passage that runs all the way around the inside of the keep . Flint ' s design was not repeated in any other castle built by Edward I in North Wales . The layout at Flint remains unique within the British Isles . History . Flint was the first castle of what would later become known as Edward I ' s " Iron Ring " . A chain of fortresses designed to encircle North Wales and oppress the Welsh . Its construction began almost immediately after Edward I began the First Welsh War in 1277 . Five years later Welsh forces under the command of Dafydd ap Gruffydd , brother of Llywelyn the Last besieged the castle in an attempted uprising against the English Crown . In 1294 Flint was attacked again during the revolt of Madog ap Llywelyn ; this time the constable of the castle was forced to set fire to the fortress to prevent its capture by the Welsh . The castle was later repaired and partly rebuilt . With the conclusion to the Welsh Wars , English settlers and merchants were given property titles in the new town that was laid out in front of the castle . The plantation borough was protected by a defensive ditch with a wooden palisade on earth banking . Its outline remains visible in streets patterns . In 1399 Richard II of England was held by Henry Bolingbroke at Flint before being returned to London . During the English Civil War , Flint Castle was held by the Royalists . It was finally captured by the Parliamentarians in 1647 after a three - month siege . To prevent its reuse in the conflict , the castle was then slighted in accordance with Cromwell ' s destruction order . The ruins are what remain today . By the 19th century part of the site ' s outer bailey was used as Flintshire ' s County Jail . A quarry also operated nearby . Present day . Flint Castle , which has been managed as public monument for 90 years , is now maintained by Cadw , a Welsh - government body that protects , conserves and promotes the building heritage of Wales . Access is free and via a path . Most parts of the castle , such as the isolated keep , are open to the public . In mid August 2009 , the agency temporarily closed Flint Castle to the public because of problems with anti - social behaviour . Cadw said youths were drinking on the site and vandalising the castle . Cadw is now liaising with North Wales Police to improve security at the castle . Later works . In 1838 J . M . W . Turner painted a watercolour of the castle . HMS " Flint Castle " ( K383 ) was a Royal Navy Castle class corvette launched in 1943 , named after Flint Castle .