Control of the Areas to the North of Cibwr was a problem facing Gilbert de Clare in the second half of the thirteenth century .
In 1266 he had taken Gruffydd ap Rhys (ruler of Uwch-and Is-Caiach) a prisoner.
Then In 1268 he started building Caerphilly Castle. In 1270 these structures were razed to the ground by the army of Llywelyn ein Llyw olaf.

De Clare took his case to Henry III and arbitrator the Archbishop of York
. He then seized the opportunity of the truce and resumed building the present castle on the 1st June 1271.Llywelyn again brought his army to Caerphilly, but the intervention of Henry III who urged another conference withheld another attack

One of Henry III's most powerful and ambitious barons, Gilbert de Clare, lord of Glamorgan, built this castle in 1270. His purpose was to secure the area and prevent lowland south Wales from falling into the hands of the Welsh leader Llywelyn the Last, who controlled most of mid and north Wales and he had taken Gruffydd ap Rhys (ruler of Uwch-and Is-Caiach) a prisoner. Then In 1268 he started building Caerphilly Castle.. De Clare built other castles on the northern fringes of his territory for the same purpose, such as Castell Coch. He had seized the upland district of Senghenydd, in which Caerphilly lies, from the Welsh in 1266 to act as a buffer against Llywelyn's southward ambitions.

 Llywelyn realised the threat and tried but failed to prevent the castle from being built; it was begun on 11 April 1268, was attacked by Llywelyn in 1270, and was begun again in 1271. This time it was completed without hindrance. Its message was not lost on Llywelyn, who retreated northwards. Apart from the remodelling of the great hall and other domestic works in 1322-6 for Hugh le Despenser, no more alterations were carried out, making it a very pure example of late 13th-century military architecture.  In 1270 these structures were razed to the ground by the army of Llywelyn ein Llyw olaf.

The design is a double-skinned parallelogram surrounded by large-scale water defences
. The concentric arrangement was more flexible than earlier plans. It gave easy access to any part of the castle by mural passages and wall-walks etc, towers and gatehouses would be independently held, attackers could be well covered and there was little possibility of mounting siege engines against the inner walls.

 The East Gatehouse used as residential quarters, and providing excellent defence in it's own right, and set a trend continued by King Edward I at Harlech and Beaumaris Castles. When one enter's the Inner Ward through the East Gatehouse, along the south curtain wall, you can see the remnants of the pale cream stonework that indicate's where the Great Hall once stood.

 Although building of the Great Hall took place over two phases, what survives dates mainly from the 14th century. The North East Tower of the inner curtain wall is sadly now in ruins, and the South East Tower has split vertically at an angle producing a very noticeable lean. which manages to out-lean even the Tower of Pisa (Tuscany, Italy) known as "The Leaning Tower

This Edwardian style castle was completed approximately ten years after building work commenced, and is a fine example of advanced military architecture with its combination of land and water defences, including an enormous barrage that also acted as a dam to the east of the castle.
 Each of the towers and gatehouses were constructed as independent forts, well able to easily defend themselves.
The castle’s strength is indicated by the presence of numerous portcullises. features of this formidable fortress include the splendid Great Hall and the ruined tower - victim of subsidence Caerphilly is considered to be the earliest and possibly the finest example of of a true regular concentric fortification in the British Isles.
 The castle is vast in size, spread over some 30 acres of land. This makes it the second largest castle in the UK after Windsor castle.