Geraint

Historically, Geraint was a prince of Dumnonia at the time of Arthur ( Dyfeint in Welsh/ Devon in English ). 

Elegy for Geraint

"Before Geraint, the enemy's scourge,

I saw white horses, tensed, red,

After the war cry, bitter the grave....

In Llongborth, I saw the clash of swords,

Men in terror, bloody heads,

Before Geraint the Great, his father's son.

In Llongborth I saw the spurs

And men who did not flinch from spears,

Who drank their wine from glass that glinted....

In Llongborth I saw Arthur's

Heroes who cut with steel.

The Emperor, ruler of our labour.

In Llongborth Geraint was slain.

Heroes of the land of Dyfeint,

Before they were slain, they slew.

Under the thigh of Geraint swift chargers,

Long their legs, wheat their fodder,

Red, swooping like milk white eagles....

When Geraint was born, Heaven's gate stood open;

Christ granted all our prayers;

Lovely to behold, the glory of Britain.

'The poem is not early; it's language is not that of the early Welsh poems, and no Welsh poem could be anywhere as old as Arthur's time, for the profound changes that turned the British language into Welsh did not take place until about a century after the death of Geraint. Any elegy composed in or about the time of Arthur would have been in British not Welsh. But the poem has nothing in common with the twisted concepts of Arthur current in the eighth and ninth centuries. It is fresh and vigorous, shot through with a sense of personal loss, as close to it's hero as are the laments for the late sixth-century heroes of Gododdin and of Rheged. It vividly describes a battle, fought as battles were fought in the fifth and sixth centuries, before the final English conquest, not in the manner of Welsh battles thereafter. The genealogies record its hero Geraint, prince of Dumnonia, now called Dyfneint in Welsh, Devon in English. The poem reads like a late written version of an older Dumnonia poem, originally composed while the memory of it's late hero still green, it's language modernised and translated from British into Welsh as the original wording became difficult and archaic.
The English tradition dates that battle to about 480. The Welsh poem puts it.....somewhere between the 470s and the 490s.'

from The Age of Arthur by John Morris, p104.

The site of the battle, obviously somewhere in the south-west of Britain, has never been successfully identified.

Early Welsh 'Llong-' is usually translated as 'ships' and '-borth' as port

Triad 14  names the 'Three Seafarers of the Island of Britain' 

"Geraint son of Erbin,

and Gwenwynwyn son of Naf,

and March son of Meirchiawn.

Sources of information on Geraint

The Marriage of Geraint by Alfred, Lord Tennyson

Geraint and Enid by Alfred, Lord Tennyson

Erec and Enid by Chretien de Troyes