The Castle That Moved a River: Edward I and the Forfardyke

Rhuddlan Castle stands several miles from the sea, on a river that was once too shallow and winding for ships. Between 1277 and 1280, Edward I had the River Clwyd cut into a new, straighter channel, the Forfardyke, so that supply ships could sail from the sea to the castle dock.

Key Facts

• The works: The Forfardyke, a new channel of about two miles for the River Clwyd
• Dates: 1277 to 1280, alongside the building of the castle
• Workforce: Hundreds of ditch-diggers, many of them fenmen from Lincolnshire
• Purpose: To let sea-going ships supply the castle, whatever happened on the roads around it
• Defended by: A river dock guarded by Gillot's Tower and a wall of arrowloops

Imagine standing on a patch of high ground in North Wales in 1277, looking out over a meandering, shallow river that does not quite go where you need it to. Most people would see a landscape. Edward I of England saw a logistical problem, and an opportunity.

He did not simply want to build a castle. Instead, he set out to reshape the land itself, ensuring his "Iron Ring" of fortresses could never be starved into submission.

Why Edward I Needed a River

Edward chose Rhuddlan for its ford across the River Clwyd, a crossing that had been fought over since at least 795 AD and that opened the way into the heart of North Wales. The full story of that choice, and of the concentric fortress he built there, is told in Rhuddlan Castle: Edward I's Fortress of Conquest. But the ford came with a problem. The castle stood about three miles inland, and the Clwyd between Rhuddlan and the sea was shallow and looped back on itself. It was no use to ships.

That mattered, because Edward fought his Welsh wars from the sea. In 1277 his army pushed along the North Wales coast with the support of ships from the Cinque Ports, and by August he had moved his forces to Rhuddlan, which he supplied by river. Food, timber, stone, weapons and men were far easier to move by ship than along roads through hostile country, where a single ambush could cut a supply line. A castle that ships could reach could be fed and reinforced whatever happened on land. A castle that they could not reach could be starved.

So Edward did not adapt his castle to the river. He adapted the river to his castle. This fits the wider logic of why there are so many castles in North Wales: almost every one of Edward's great fortresses was placed where it could be reached from the water.

Cutting the Forfardyke

Edward's answer was the Forfardyke. Between 1277 and 1280, hundreds of ditch-diggers, many of them fenmen from Lincolnshire, cut a new, straighter and deeper channel of about two miles, so that ships could sail from the sea up to the castle.

The fenmen were chosen for a reason. They came from a landscape of drains, dykes and waterlogged ground, and they knew how to cut and shape channels in soft, wet earth better than almost anyone in the kingdom. Their work replaced the river's old, looping course with a channel that was straightened and dredged until it could carry sea-going vessels. Cadw describes the result as the Clwyd canalised for more than 3.5 kilometres so that Rhuddlan could be constantly supplied by sea.

The digging ran alongside the building of the castle itself, and took about three years. It was one of the most ambitious engineering projects of Edward's first Welsh campaign, and it shows how far he was prepared to go: rather than accept the limits of the landscape, he paid to rewrite them.

Photographs of the River Clwyd taken by Simon Williams (April 2026)

All photographs © Simon Williams, April 2026

Where the Ships Docked: Gillot's Tower and the River Wall

The new channel brought ships right to the foot of the castle. On the river side, the outer ward ran down the slope to the water and enclosed a protected dock. Guarding it was Gillot's Tower, a square tower of four storeys with a small gate, or postern, beside it, and a river wall pierced with arrowloops. Cadw's own visitor material puts it simply: the tower protected the dock and the ships that carried the castle's supplies.

Blueprint Illustration of Rhuddlan Castle

The river was part of the castle's defences as well as its lifeline. A broad, stone-lined moat protected three sides of the castle, and the River Clwyd protected the fourth. The concentric design, with the tall towers of the inner ward rising behind the lower outer wall, meant that anyone trying to reach the dock from the land side had to get through both rings of defence first.

Why a River Made Rhuddlan Hard to Starve

This was a logistical masterstroke. By ensuring the castle could be resupplied by sea (which the English controlled), Edward made Rhuddlan virtually immune to land-based sieges by Welsh forces. Provisions and troops could reach the castle even if hostile forces held every road around it. It was a literal reshaping of the Welsh landscape to serve English military interests.

It was also expensive. The castle was completed in 1282 at a cost of £9,613, more than the later, world-famous Harlech Castle, and the river works were part of the same royal investment. Edward was not building a fort for a single campaign. He was building a permanent base that could hold the Clwyd valley for as long as the English controlled the sea.

What the River Made Possible

With its supply line secure, Rhuddlan became the centre of English power in north-east Wales. A new town was laid out beside it, chartered in 1278 and settled mainly by English colonists, and its grid of streets can still be traced today. And in March 1284, after the death of Llywelyn ap Gruffudd and the final conquest of Gwynedd, Edward issued the Statute of Rhuddlan here, bringing English common law to Wales and creating new English-style shires.

Illustration of The Statute of Rhuddlan

None of that was inevitable. It rested on a castle that could not be starved, and that castle rested on a river that had been dug for it.

The River Today

The straight channel cut in the thirteenth century still carries the Clwyd below the castle, and on aerial photographs it is still possible to make out traces of the river's older loops in the surrounding fields. From the castle, the straight line of the river running towards the sea is the clearest surviving sign of Edward's engineers at work.

A Timeline of Power at Rhuddlan

To help you digest the scale of this medieval project, we've synthesised the key data into scannable formats.

Timeline for Rhuddlan Castle

Concluding Thoughts

Rhuddlan Castle is usually remembered for its towers and for the Statute of Rhuddlan, but its most remarkable feature may be the river beneath its walls. By moving the Clwyd, Edward I turned an inland site into a castle the sea could reach, and a fortress that could have been starved into one that could hold a valley. It is a reminder that medieval conquest was won as much with spades and supply ships as with swords.

Sources

• Exploring Rhuddlan Town Trail: Mentions the strategic spot at the ford of the River Clwyd being a flashpoint since 795 AD and the Saxon defeat of the Welsh.
• Rhuddlan Town Plan: Notes the importance of the ford for controlling invasion routes into North Wales.
• Castell Rhuddlan | Cadw: Identifies it as the first of the revolutionary concentric, or "walls within walls," castles designed by James of St George.
• VisitWales: Confirms the inner diamond-shaped stronghold and twin-towered gatehouses sitting inside a ring of lower walls.
• The Edwardian Conquest and its Military Consolidation: Notes that the river was diverted specifically to link the castle to the sea.
• The Slighting: Information regarding the castle being rendered untenable and "slighted" in 1648 following the English Civil War.
• Castell Rhuddlan visitor leaflet (Cadw): Describes the Clwyd canalised for more than 3.5 km so the castle could be supplied by sea, and Gillot's Tower guarding the dock and supply ships.
• Rhuddlan Castle (Wikipedia): Notes the 1277 advance along the coast with ships of the Cinque Ports, and Edward supplying Rhuddlan by river.

This article is part of the Castles in Wales series and our wider guide to the castles of England and Wales.

Deepen Your Understanding

• Rhuddlan Castle: Edward I's Fortress of Conquest: The full history of the castle, from the ancient ford to the Civil War slighting.
• The Significance of the Statute of Rhuddlan in Edward I's Control Over Wales: How a single piece of legislation reshaped the political map of medieval Britain.
• Flint Castle: Edward I's First Welsh Fortress: The Iron Ring began at Flint, just eight miles up the coast from Rhuddlan, and this article tells that story.
• Caernarfon Castle: The Imperial Fortress: The most ambitious castle in Edward's Iron Ring, and the birthplace of the prince the Rhuddlan tradition speaks of.
• Why Are There So Many Castles in North Wales?: The broader strategic logic behind the Iron Ring, explained.
• Visiting Rhuddlan Castle: Parking, tickets, opening times and the walk to Twthill.

People Also Ask

Did Edward I really move a river to build Rhuddlan Castle?

Yes. Between 1277 and 1280, hundreds of ditch-diggers, many of them fenmen from Lincolnshire, cut the Forfardyke, a new, straighter and deeper channel of about two miles, so that the River Clwyd ran directly beside the castle and was deep enough for sea-going vessels. The Clwyd had previously been too shallow and too winding to allow ships to reach the site. Once the channel was complete, English supply fleets could sail straight from the Irish Sea to the castle dock, bypassing any Welsh blockade on land routes. The redirected river is still part of the landscape today.

What was the Forfardyke?

The Forfardyke was the new channel cut for the River Clwyd between Rhuddlan and the sea on the orders of Edward I. Dug between 1277 and 1280, it replaced the river's shallow, looping course with a straighter and deeper channel of about two miles. Cadw describes the work as canalising the Clwyd for more than 3.5 kilometres so that Rhuddlan could be supplied by sea. Some modern accounts call the works the Great Ditch.

Who dug the new channel for the River Clwyd?

The digging was done by hundreds of ditch-diggers brought to Rhuddlan by the Crown, many of them fenmen from Lincolnshire, who were skilled at cutting and draining channels in wet, low-lying ground. They worked on the river for about three years, from 1277 to 1280, alongside the masons and carpenters building the castle itself.

Why did Rhuddlan Castle need to be supplied by sea?

Edward I's armies relied on supplies brought along the coast by ship, because moving food, timber, stone and weapons overland through hostile country was slow and easily cut off. In 1277 his army advanced along the north Wales coast with the support of ships from the Cinque Ports, and he supplied Rhuddlan by river. A castle that could be reached from the sea could be provisioned and reinforced even if Welsh forces held every road around it.

How did ships reach Rhuddlan Castle?

Ships sailed in from the Irish Sea and up the new channel of the River Clwyd to a protected dock on the river side of the castle. The outer ward ran down the slope to the water, and the dock was guarded by Gillot's Tower, a square tower with a small gate beside it, and by a river wall pierced with arrowloops. The castle's broad moat protected the other three sides, while the river itself formed the fourth.

Can you still see where the River Clwyd used to flow?

Yes. The straight channel cut in the thirteenth century still carries the Clwyd below the castle today, and on aerial photographs and satellite images it is still possible to make out traces of the river's older loops and bends in the surrounding fields. From the castle walls, the straightness of the channel running towards the sea is easy to see.

Relevant Exam Boards & Specifications

This article supports UK GCSE and A-Level History modules covering the Edwardian conquest of Wales, medieval military engineering, and royal logistics:

• AQA GCSE History (8145)

  Paper 2: Section A, Britain: Power and the People: c1170 to the Present Day / Conflict and Tension

  Module Focus: Explores the expansion of royal authority under Edward I, the suppression of native Welsh principalities, and the logistical supply lines required to sustain military campaigns in hostile territory.

• Edexcel GCSE History (1HI0)

  Paper 2: Option 11, Medieval Depth Study: Crown and Authority in Late Medieval England

  Module Focus: Details the strategic deployment of Edward I's iron ring of castles, focusing on the engineering feats, river diversion projects, and maritime logistics used to supply Rhuddlan Castle.

• OCR A Level History A (H505)

  Unit Y108: The Early Plantagenets 1154 to 1377 / British Period Studies

  Module Focus: Provides critical analysis of Plantagenet warfare, royal expenditure, administrative organisation, and the innovative architectural and civil engineering methods overseen by Master James of St George.

• WJEC / Eduqas A Level History

  Component 1: Depth Study, Government, Rebellion and Society in Wales and England c.1215 to 1307

  Module Focus: Focuses specifically on the conquest of Gwynedd, the establishment of English boroughs at Rhuddlan alongside the Statute of Rhuddlan (1284), and the reshaping of the Welsh landscape.

Who Would Benefit from Reading This?

• GCSE History Students: Ideal for visualising the immense scale of engineering and logistics involved in Edward I's conquest of Wales, including the radical altering of natural watercourses.
• A-Level History Students: Essential for exploring medieval civil engineering, military supply chains, and the strategic establishment of fortified administrative centres in conquered regions.
• Teachers & Educators: Valuable as an engaging reference guide for lessons on medieval architecture, the River Clwyd engineering works, and the foundational role of Rhuddlan in the Edwardian war machine.

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