Once there was an old giant in Wales called Gwendol Wrekin ap Shenkin ap Mynyddmawr. He had a very great spite against the town of Shrewsbury. He therefore made up his mind to dam up the River Severn and cause such a flood that the town would be drowned. 
Off he set, carrying a giant-sized spadeful of earth, and tramped along mile after mile trying to find the way to Shrewsbury. But he missed it. At last he got close to Wellington. By that time he was puffing and blowing under his heavy load, and wished he was at the end of his journey.
Soon there came a cobbler along the road. He was carrying a sack of old boots and shoes on his back, for he lived at Wellington and went once a fortnight to Shrewsbury to collect his customers' old boots and shoes and take them home with him to mend.
The giant called out to him. "I say," he said, "how far is it to Shrewsbury?"
"Shrewsbury," said the cobbler, "what do you want at Shrewsbury?"
"Why," said the giant, "to fill up the Severn with this lump of earth I've got here. I have an old grudge against the folks at Shrewsbury, and now I mean to drown them out and get rid of them all at once."
"I can't afford to lose my customers!" thought the cobbler, and spoke up again. "Eh!" he said, "you won't get to Shrewsbury today or tomorrow. Just look at me! I'm just come from Shrewsbury, and I've had time to wear out all these old boots and shoes on the road since I started." Then he showed the giant his sack.
"Oh!" said the giant, with a great groan, "then it's no use! I'm fairly tired out already, and I can't carry this load of mine any farther. I shall just drop it here and go back home." So he dropped the earth on the ground just where he stood, and scraped his boots on the spade, and off he went home again to Wales, and nobody ever heard anything of him in Shropshire again. But where he put down his load there stands the Wrekin to this day; and even the earth he scraped off his boots was such a pile that it made the smaller Ercall Hill nearby.
[Hartland 1890, p. 85-86.]
Wales is one of the four countries of the United Kingdom, and the Red Dragon is a national symbol of Wales. Why is that dragon red, and not white, yellow, green, purple, blue, or pink? And why does it have four three-toed claws, a long, barbed tongue, a tail ending like an arrow head, and wide, unfolded wings?
The colour red is, among other things, a colour of blood. The red dragon is made the way it is, colour and all, to suggest that it is ready to battle for and guard the Welch (Cymric) people. The Welch are the oldest of the British peoples, with Druids, bards, and chiefs in a history that goes back to remote times. Many Welch fairy tales have roots in ancient, hazy mythology.
After the Romans in the south of Britain had left the island, the Cymric king, Vortigern, was hard pressed by the Picts and Scots of the north. Then he decided to get people from the tribes called the Long Knives, Saxons, to help him as mercenaries. And mercenaries came, from beyond the North Sea. But once on the big island, they would not go back. They wanted to remain in Britain.
Vortigern soon found out that the Long Knives would soon attack him, he called his twelve wise men together to get their advice. With one voice, they advised him to retreat westward behind the mountains into Cymru. There he must build a strong fortress and defy his enemies.
The Saxons drove the Cymry beyond the western borders of England and into what they named the foreign or Welsh parts. Centuries afterwards, after the fifth century, these tracts got the name of Wales.
The place chosen for the fortified city of the Cymry was among the mountains. From all over his realm, the king sent for masons and carpenters and gathered the materials for building. Then, with harp music and songs, some white-bearded Druid priests dedicated the spot as a stronghold of the Cymric nation.
The king set the diggers to work. He promised a rich reward to those who should dig the fastest and throw up the most dirt, so that the masons could begin their part of the work as early as possible.
But during the night everything that was of stone, timber, iron or tools, disappeared. King and seers, priests and bards, were greatly puzzled at this. However, the king set the diggers at work and again collected more wood and stone. This time, even the women helped, not only to cook the food, but to drag the logs and stones. But in the morning, all had again disappeared and the ground was bare.
For the third time the work began anew. Yet when the sun rose next morning, there was not even a trace of either material or labour. Vortigern again summoned his twelve wise men to meet in council to try to find out why this happened and decide what could be done.
While all the workmen and people outside waited for their verdict, the wise men agreed after long deliberation on a remedy, such as sacrificing a human being. This was done either by walling up the victim while alive, or by mixing his or her blood with the cement used in the walls. Often it was a virgin or a little child chosen by lot and made to die for good luck. The idea was to ward off anger of invisible entities or to appease dragons under ground, and also to make the workmen do their best.
So nobody was surprised when the king announced: "A child must be found who was born without a father. He must be brought here and put to death. Then his blood will be sprinkled on the ground and the citadel will be built securely."
Within an hour, swift runners bounded over the Cymric hills in search of a boy without a father, and a large reward was promised to the one who found what was wanted. One messenger noticed some boys playing ball. Two of them were quarreling. Coming near, he heard one say to the other: "Ambrosius, you fatherless boy, nothing good will ever happen to you."
"This must be the one looked for," said the royal messenger to himself. So he went up to the boy who had been taunted and spoke to him thus: "Don't mind what he says." Then he added that great things would happen if the boy would go along with him.
The boy was glad to go, and the next day the lad was brought before King Vortigern and the thousands who had gathered for the ceremony where a boy's blood was to be shed.
The boy asked the king, "Why have your servants brought me to this place?"
The sovereign told him the reason, and the boy asked, "Who instructed you to do this?"
"My wise men told me so to do, and even the sovereign of the land obeys his wise councilors."
"Order them to come to me," pleaded the boy.
When the wise men appeared, the boy asked them, "How was the secret of my life revealed to you? Please speak freely and declare who it was that discovered me to you."
Turning to the king, the boy added, "Pardon my boldness. I shall soon reveal the whole matter to you, but I first want your advisers to tell you what is the real cause, and reveal what is hidden underground here if they can."
But the wise could not tell it.
The boy then said, "There is a pool of water down below. Please order your men to dig for it."
At once the spades were plied by strong hands, and in a few minutes the workmen found a pool of clear water.
Turning to the wise men, the boy asked before all, "Now tell me, what is in the pool?"
Now thoroughly ashamed, the wise men were silent.
"King, I can tell you, even if these men cannot. There are two vases in the pool."
Two brave men leaped down into the pool. They felt around and brought up two vases, as the boy had said.
Again, the lad put a question to the wise men, "What is in these vases?"
Once more, those who professed to know the secrets of the world, even to the demanding of the life of a human being, held their tongues.
"There is a tent in them," said the boy. "Separate them, and you will find it to be so."
By the king's command, a soldier thrust in his hand and found a folded tent.
"What is in the tent?" asked the boy of the wise men.
Not one of the twelve knew what to say, and there was an almost painful silence.
"I will tell you all here what is in this tent. There are two serpents, one white and one red. Unfold the tent."
Two stalwart fellows stepped forward to open the tent. A few of the men and many of the women shrank back while those that had babies, or little children, snatched up their children, fearing that the poisonous snakes might wriggle towards them.
The two serpents were coiled up and asleep, but they soon showed signs of waking, and their fiery eyes glared at the people.
"Now, king, and all here, witnesses what will happen. Let the king and wise men look in the tent."
At this moment, the serpents stretched themselves out at full length, while all fell back, giving them a wide circle to struggle in.
Then they reared their heads. With their glittering eyes flashing fire, they began to struggle with each other. The white one rose up first, threw the red one into the middle of the arena, and then pursued him to the edge of the round space.
Three times the white serpent gained the victory over the red one. But while the white serpent seemed to be gloating over the other for a final onset, the red one, gathering strength, lifted its head and struck at the other.
The struggle went on for several minutes, but in the end the red serpent overcame the white, driving it first out of the circle, then from the tent, and into the pool, where it disappeared while the victorious red one moved into the tent again.
When the tent flap was opened for all to see, nothing was visible except a red dragon; for the winning serpent had turned into this creature which combined in one new form the body and the powers of bird, beast, reptile and fish. It had wings to fly, the strongest animal strength, and could crawl, swim, and live in either water or air, or on the earth.
Then, in the presence of all the assembly, the youth turned to the wise men to explain the meaning of what had happened. But they did not speak a word, and looked ashamed.
"Now, king, let me reveal to you the meaning of this mystery."
"Speak on," said the king gratefully.
"This pool stands for the world, and the tent for your kingdom. The two serpents are two dragons. The white serpent is the power of the Saxons, who now occupy several of the provinces and districts of Britain and from sea to sea. But when they invade our soil our people will finally drive them back and hold fast their beloved Cymric land. But you must choose another site to build your castle on."
After this, whenever a castle was to be built, no more human victims were doomed to death. All the twelve men, who had wanted to keep up the old cruel custom, were treated as deceivers of the people. Today, these men are remembered only by the Twelve Mounds on a field hard by.
As for the boy, he lived long on the mountain, but when he went away from there with a friend, he placed all his treasures in a golden cauldron and hid them in a cave. He rolled a great stone over its mouth. Then with sod and earth he covered it all over so as to hide it from view. He wanted to leave this his wealth for a leader who would use it for the benefit of his country in some future generation, when most needed. When such a special person comes to Denas, a bell will ring to invite him into the cave. The moment his foot is over the place, the stone of entrance will open of its own accord, and he can then carry away the treasure.
[Griffis 1921, p. 47-59. 'The Great Red Dragon of Wales'. Retold.]
A. Cymru and Cymric.
B. Histories are often about rulers, and some histories are contracted by rulers. In many ancient works of history, facts are rather sparse, while legends and myths may abound, intermingle, and get altered in time. It often happens. And there may be several, markedly different versions too. Such things should be expected.
Many British tales were remade and edited many times, to suit rulers, among others. The Historia Brittonum, or The History of the Britons, is a historical work that was first composed around 830 CE. The prevalent view by historians is that the text was composed for Merfyn Frych ap Gwriad, king of Gwynedd, who ruled about 825-844). The text purports to relate the history of the Brittonic inhabitants of Britain from earliest times. The reliability of the work has been questioned both in part and in whole, and professor David Dumville believes that this text has been enlarged and rewritten many times and in many ways between the date of its apparent origin, and the date of its surviving manuscripts.
The Historia Brittonum is the earliest source that presents Arthur as a historical figure, and is the source of several stories that were repeated and amplified by later authors through legends and myths of a King Arthur.
The Historia also contains the story of the king Vortigern, who allowed the Saxons to settle in the island of Britain in return for the hand of Hengest's daughter. According to British legend, Hengest and his brother were two Germanic brothers who led the Angle, Saxon, and Jutish armies that conquered the first territories of England in the 5th century CE. And Hengist is traditionally listed as the founder of the Kingdom of Kent.
According to the old British sources, Hengist and Horsa arrived in Britain as mercenaries serving Vortigern, King of the Britons. This soon led to the Anglo-Saxon invasion of Britain. In the Historia Brittonum Hengist had an unnamed daughter who seduced Vortigern, and eventually lead to the Night of the Long Knives when Hengist's men massacred the Britons at a peace accord.
One legend recorded of Vortigern concerns his attempt to build a stronghold near Snowdon, called Dinas Emrys, only to have his building materials stolen each time he tried. His advisers told him to sprinkle the blood of a boy born without a father on the site to lift the curse. Vortigern found such a youth in Aurelius Ambrosius, who rebuked the wise men and revealed that the cause of the disturbance was two serpents buried under the ground. Ambrosius later had disputes against Vortigern and is mentioned as a high king later in the story.
The tower story is repeated and embellished by Geoffrey of Monmouth in his Historia Regum Britanniae
C. Ambrosius Aurelianus, a source of "Merlin"
At the end of the story in Chapters 40 – 42, Vortigern hands over to Ambrosius "the fortress, with all of the kingdoms of the western part of Britain." In Chapter 48 Ambrosius Aurelianus is described as "king among all the kings of the British nation." So it is possible that he ruled some part of what is now England.
The story about Ambrosius, Vortigern, and the two dragons was later retold with more detail by Geoffrey of Monmouth in his fictionalized Historia Regum Britanniae, where he made up a Merlin character by forging Ambrosius with another.
There are other smaller snippets of tradition in the Historia too: in Chapter 31 it says that Vortigern ruled in fear of one Ambrosius. Because Ambrosius and Vortigern are shown in the Historia Brittonum as being in conflict, some historians have suspected that this preserves a historical core of two parties in opposition to one another, one headed by Ambrosius and the other by Vortigern.
Sources: Wikipedia, s.v. "Historia Brittonum," "Ambrosius Aurelianus," "Hengist and Horsa," "Geoffrey of Monmouth," "Wales," and "Merlin."