How they worked

D-shaped towers and walls within walls

How Welsh-built castles used their rocks, and how Edward I’s builders made rings of walls, gatehouses and walled towns.

Jump to: Welsh castles | Tower shapes | Walls within walls | Building them | The sea

How the Welsh built

Unlike the geometric English fortresses, Welsh castles tend to be irregular, made to fit their rocky settings. Cadw: More about Castell Dolwyddelan Deep rock-cut ditches often strengthened their natural defences. Cadw: More about Castell Dolwyddelan

Welsh castles had lower walls, and characteristic D-shaped (not round) towers that were the real strongholds. Cadw: More about Castell Dolwyddelan

Its curtain walls are made of unmortared slate slabs. Cadw: Castell Dolbadarn

Tower shapes

A Welsh D-shaped tower is rectangular with one half-rounded end: a roomy living chamber, with a wide field of fire from the rounded end. Cadw booklet: The Castles of the Lords and Princes of Wales (PDF)

Cadw calls Dolbadarn the finest surviving example of a Welsh round tower. Cadw booklet: The Castles of the Lords and Princes of Wales (PDF) Llywelyn’s castle had a two-storey rectangular keep, with the main chamber above an unlit basement. Cadw booklet: The Castles of the Lords and Princes of Wales (PDF)

Criccieth’s great gatehouse, with D-shaped towers, was built by Llywelyn the Great; his grandson added the outer ward. Cadw: Castell Cricieth

Walls within walls

Concentric castles have “walls within walls”: an inner ring of defences inside an outer one. Cadw: Castell Rhuddlan Rhuddlan, begun in 1277, was the first of James of St George’s concentric castles. Cadw: Castell Rhuddlan

It has four rings of defences, a water-filled moat with its own dock, and 300 arrow loops in the outer walls. Cadw: Beaumaris Castle

UNESCO lists the features still on show: barbicans, drawbridges, fortified gates, chicanes, redoubts, dungeons, towers and curtain walls. UNESCO World Heritage Centre: Castles and Town Walls of King Edward in Gwynedd

Its entrance, with two gate-towers each with a drawbridge, was very advanced for its time, even by English standards. Cadw: More about Castell y Bere

Building them

James of St George (about 1230–1309) was Edward I’s chief architect; UNESCO calls him the greatest military architect of the age. UNESCO World Heritage Centre: Castles and Town Walls of King Edward in Gwynedd The building of these royal castles is fully documented: the accounts name where the workmen came from, from all over England. UNESCO World Heritage Centre: Castles and Town Walls of King Edward in Gwynedd

At Conwy, master mason James of St George raised the towers and curtain wall first, then built the royal apartments inside. Cadw: More about Castell Conwy

Conwy’s castle and town walls were built in about four years, between 1283 and 1287. Cadw: Castell Conwy Harlech was finished from ground to battlements in just seven years. Cadw: Castell Harlech

Castle, town walls and quay were built at the same time; the project took 47 years and cost £25,000. Cadw: Castell Caernarfon Rhuddlan was completed in 1282 at a cost of £9,613. Cadw: More about Castell Rhuddlan

Traces of lime render show that Conwy Castle was originally white. Cadw: More about Castell Conwy

Its many-sided towers, eagle statues and multi-coloured stonework echoed imperial Roman architecture, especially the walls of Constantinople. Cadw: Castell Caernarfon They also recalled the Welsh story of Macsen Wledig, who dreamed of a great fort at the mouth of a river. Cadw: Castell Caernarfon

Supplied by sea

Edward I liked his castles on the coast, so supplies could still arrive by sea if a campaign ran into trouble. Cadw: Castell Rhuddlan Hundreds of ditch-diggers deepened and moved the River Clwyd so ships could reach Rhuddlan. Cadw: Castell Rhuddlan

When cut off by the rising of Madog ap Llewelyn, Harlech was supplied by ship up the “Way from the Sea”, a path of 108 steps. Cadw: Castell Harlech

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