Armes Prydein Fawr, the Great Prophecy of Britain, is a poem attributed to Taliesin (although could not be his work as it was composed in the 10th century) in which he sings of the return of Cadwaladr ap Cadwallon (the hero in my book, The Last Pendragon) and Cynan, another dark age leader of the Welsh people.  Among the Welsh, it was these two, not Arthur, who would return in the future to save Britain.  The motivation was the same, however, in that the poet desires to drive the invading Saxons out of the land that had belonged to the Cymry.

In the poem, Taliesin predicts the allliance of the Irish and Scots with the Welsh towards that purpose.  John Davies, in his book, The History of Wales, writes that the poem expresses frustration with the peaceful, compromising policies of Hywel Dda (c. 930)  towards the Saxons (2007:93).  Further, the poem finds the root of its anguish in the deep sense of loss which became the motivating force behind much of Welsh mythology–the loss of their country to the Saxons after the fall of Rome (2007:48).

Cadwaladr ap Cadwallon was a King of Gwynedd, born in 633 AD.  His father, a powerful king himself who’d allied himself with Mercia in marrying Alcfrith, sister of King Penda, was killed in battle in 634.  With Cadwallon’s death, Gwynedd was left in disarray, and Cadwaladr’s people (whoever they were–there is no record of what happened to Alcfrith so perhaps she died in childbirth), fled Gwynedd with him.  His place was taken by a man named Cadfael of unknown origin.

http://www.earlybritishkingdoms.com/bios/cadwagd.html

Cadwaladr grew up and returned to overthrow the usurper, ruling from 655 to 682 AD and is recorded by Geoffrey of Monmouth as the last great King of Wales.  Consequently, anything that we ‘know’ about Cadwaladr that is based on his story, is probably apocryphal.  What is well established is that the red dragon of Wales–The Red Dragon of Cadwaladr–is attributable to him.

Far less is known about Cynan, who ruled in the middle/late 6th century Powys in the east and southeast of Wales.

http://www.earlybritishkingdoms.com/bios/cynangpw.html

From Taliesin’s poem (not a fabulous translation, but a free one

http://www.maryjones.us/ctexts/t06.html):

With sharp-ground blades utterly they will kill.
There will be no advantage to the physician from what they do.
The armies of Cadwaladyr, mighty they come,
The Cymry were exalted, a battle they made.
A slaughter without measure they assailed.
In the end of their taxes, death they know.
0thers, large branches they planted.
For age of ages their taxes they will not leave off.
In wood, in plain, on lull,
A candle in the dark will go with them.
Cynan opening a forward way in every descent.
Saxons against the Brython, woe they will sing.
Cadwaladyr a pillar with his princes.
Though prudence utterly attending to then.
When they drop their covering over their support.
In affliction, and the crimson gore on the cheeks of the Allmyn.
At the end of every expedition spoil they lead.

Also included in the Book of Taliesin is an enigmatic poem, cut off almost before it begins.  It is called The Prediction of Cadwaladr.

The knight of the swift bay horse
with the double face, creates turmoil:
With treachery afoot, a blessing his
death and burial in Snowdonia.
When our war-lord comes he will make,
in a mead in Prydein, a chief place.
His manifest life will invigorate morals:
and his confines will be to us an Eden.
There will come, thither,
A Saxon seeking hospitality.
Grief he will know; from excess
of presumption, he will sin
The yoking of a wife by a vassal
will renew old hatred: he will
know grief: from presumption
comes contempt; he commits treason.
Did you see my friend
playing with my spouce?
I saw a slim corse,
and crows full of activity.
But the catastrophe lacks the prostrate form
of the sword-stroke.
And beyond the bank of…  (the manuscript is cut off)