Before the English built the town of Conwy, Aberconwy Abbey, the site was occupied by a Cistercian monastery favoured by the Welsh princes, as well as the location of one of the palaces (called llys) of the Welsh princes.
From Conwy: "...the oldest structure is part of the town walls, at the southern end of the east side.
Here one wall and the tower of a llys [palace/court house] belonging to Llywelyn the Great and his grandson Llywelyn ap Gruffydd have been incorporated into the wall.
Built on a rocky outcrop, with an apsidal tower, it is a classic, native, Welsh build and stands out from the rest of the town walls, due to the presence of four window openings.
It dates from the early 13th century and is the most complete remnant of any of his Llys."

The location also controlled an important crossing point over the River Conwy between the coastal and inland areas of North Wales, that Deganwy Castle for many years had defended.
The kings of England and the Welsh princes had vied for control of the region since the 1070s and the conflict had resumed during the 13th century, leading to Edward I intervening in North Wales for the second time during his reign in 1282.

Edward invaded with a huge army, pushing north from Carmarthen and westwards from Montgomery and Chester.
Edward captured Aberconwy in March 1283 and decided that the location would form the centre of a new county: he would relocate the abbey eight miles up the Conwy valley to a new site at Maenan, establishing Maenan Abbey, and build a new English castle and walled town on the monastery's former site.
The ruined castle of Deganwy was abandoned and never rebuilt.
Edward's plan was a colonial enterprise and placing the new town and walls on top of such a high-status native Welsh site was in part a symbolic act to demonstrate English power.

Work began on cutting the ditch around Conwy Castle within days of Edward's decision.
The work was controlled by Sir John Bonvillars and overseen by master mason James of St. George, and the first phase of work between 1283 and 1284 focused on creating the exterior curtain walls and towers.
In the second phase, from 1284 and 1286, the interior buildings were erected, while work began on the walls for the neighbouring town.
By 1287, the castle was complete.
The builders recruited huge numbers of labourers from across England for the task.
At each summer building season, the labourers massed at Chester and then walked into Wales.
Edward's accountants did not separate the costs of the town walls from that of the castle, but the total cost of the two projects came to around £15,000, a huge sum for the period.

The castle's constable was, by a royal charter of 1284, also the mayor of the new town of Conwy (to this day, the Mayor is ex-officio Constable of the Castle), and oversaw a castle garrison of 30 soldiers, including 15 crossbowmen, supported by a carpenter, chaplain, blacksmith, engineer and a stonemason.
In 1294 Madog ap Llywelyn rebelled against English rule.
Edward was besieged at Conwy by the Welsh between December and January 1295, supplied only by sea, before forces arrived to relieve him in February.
Chronicler Walter of Guisborough suggested that given the austere conditions Edward refused to drink his own private supply of wine, and instead had it shared out amongst the garrison.
For some years afterwards, the castle formed the main residence for visiting senior figures, and hosted Edward's son, the future Edward II in 1301 when he visited the region to receive homage from the Welsh leaders.
Before the English built the town of Conwy, Aberconwy Abbey, the site was occupied by a Cistercian monastery favoured by the Welsh princes, as well as the location of one of the palaces (called llys) of the Welsh princes. From Conwy: "...the oldest structure is part of the town walls, at the southern end of the east side. Here one wall and the tower of a llys [palace/court house] belonging to Llywelyn the Great and his grandson Llywelyn ap Gruffydd have been incorporated into the wall. Built on a rocky outcrop, with an apsidal tower, it is a classic, native, Welsh build and stands out from the rest of the town walls, due to the presence of four window openings. It dates from the early 13th century and is the most complete remnant of any of his Llys." 
The location also controlled an important crossing point over the River Conwy between the coastal and inland areas of North Wales, that Deganwy Castle for many years had defended. The kings of England and the Welsh princes had vied for control of the region since the 1070s and the conflict had resumed during the 13th century, leading to Edward I intervening in North Wales for the second time during his reign in 1282.
Edward invaded with a huge army, pushing north from Carmarthen and westwards from Montgomery and Chester. Edward captured Aberconwy in March 1283 and decided that the location would form the centre of a new county: he would relocate the abbey eight miles up the Conwy valley to a new site at Maenan, establishing Maenan Abbey, and build a new English castle and walled town on the monastery's former site. The ruined castle of Deganwy was abandoned and never rebuilt. Edward's plan was a colonial enterprise and placing the new town and walls on top of such a high-status native Welsh site was in part a symbolic act to demonstrate English power.
Work began on cutting the ditch around Conwy Castle within days of Edward's decision. The work was controlled by Sir John Bonvillars and overseen by master mason James of St. George, and the first phase of work between 1283 and 1284 focused on creating the exterior curtain walls and towers. In the second phase, from 1284 and 1286, the interior buildings were erected, while work began on the walls for the neighbouring town. By 1287, the castle was complete. The builders recruited huge numbers of labourers from across England for the task. At each summer building season, the labourers massed at Chester and then walked into Wales. Edward's accountants did not separate the costs of the town walls from that of the castle, but the total cost of the two projects came to around £15,000, a huge sum for the period.
The castle's constable was, by a royal charter of 1284, also the mayor of the new town of Conwy (to this day, the Mayor is ex-officio Constable of the Castle), and oversaw a castle garrison of 30 soldiers, including 15 crossbowmen, supported by a carpenter, chaplain, blacksmith, engineer and a stonemason. In 1294 Madog ap Llywelyn rebelled against English rule. Edward was besieged at Conwy by the Welsh between December and January 1295, supplied only by sea, before forces arrived to relieve him in February. Chronicler Walter of Guisborough suggested that given the austere conditions Edward refused to drink his own private supply of wine, and instead had it shared out amongst the garrison. For some years afterwards, the castle formed the main residence for visiting senior figures, and hosted Edward's son, the future Edward II in 1301 when he visited the region to receive homage from the Welsh leaders.
Conwy Castle