King Edward I was known as Longshanks because of his great height.

We can safely assume that residents of 13th-century Anglesey had one or two less complimentary names for him. But they would have whispered them very carefully.

What Edward did in Beaumaris was typical of the ruthless way he stamped his authority on his newly conquered territories in Wales. He didn’t just build castles. He created English towns to go with them – and rode roughshod over centuries of Welsh culture and history.

The island of Anglesey, or Ynys Môn, held a special place in Welsh hearts long before Beaumaris was ever thought of. It was celebrated as ‘Môn mam Cymru’ (‘Mona, mother of Wales’) because of its mild climate and fertile fields. The so-called ‘bread basket of Wales’ helped to sustain the nation and support its independence.

In the early 13th century a town called Llanfaes in the south-east corner of Anglesey grew up under the patronage of Llywelyn the Great. His royal palace or ‘llys’ was nearby and he founded the first of just three Franciscan friaries in Wales there.

By the 1280s Llanfaes was a busy port trading with other towns in Britain and on the Continent. But none of this mattered to King Edward I. It was just a mile from the spot he’d identified for his new town and castle of Beaumaris. It had to go.

As soon as Edward’s troops arrived in 1295 they started to demolish Llanfaes. The frantic townspeople petitioned the king: ‘They cannot buy or sell as they used to and ships are not allowed to land in the town’s harbour. Their houses have been carried off to Beaumaris and nothing is left.’

It did no good. By Edward’s death in 1307 only a windmill, a parish church and the friary were still standing. Many of the residents were forcibly resettled in a second new town at Newborough 13 miles/20km away.

Meanwhile Beaumaris soon outstripped its doomed predecessor. It received its first royal charter in 1296 and by 1305 contained 132 ‘burgages’ or properties – making it the biggest borough in north Wales. It remained the most important town on Anglesey for most of its history.

No other new castle in north Wales saw such a massive redistribution of land. Beaumaris was the final link in the great chain of Edward’s castles stretching along the north Wales coast. By now he must have felt he could behave as he pleased.

Even in its unfinished state Beaumaris Castle combines the beauty of its perfect symmetry with an overwhelming sense of ruthless power.