Varys: Westeros has mighty rivers, but none of them compare to the Rhoyne. It is said that there is no stream or puddle in western Essos, but drains to Mother Rhoyne. No doubt an exaggeration. Until one sees the river.
At its widest, a man in the centre can't see a shore to either side. The greatest of Mother Rhoyne's children were the Rhoynar, a civilization as ancient and grand as Old Ghis. Fishers, traders, scholars, workers of wood, stone and metal, the Rhoynar raised their elegant cities from the headwaters of the Rhoyne down to her mouth, each lovelier than the last.
For many centuries, the Rhoynar lived in relative piece. When invaders swept down from the hills, the Rhoynar women and men would don silver-scaled armor, fish head helms, tall spears and turtle shell shields. If the enemy did not laugh themselves away, it was said that Mother Rhoyne would whisper the enemy's secrets to her children and the Rhoynish wizards could raise watery walls to drown their foes.
Whatever magic the Rhoynar may have had, it wasn't enough. When Valyrian colonists first arrived, the Rhoynar embraced them for all men were welcome to share the bounty of Mother Rhoyne. Perhaps a water people should have been more cautious of strangers who exulted fire and blood. Legend has it that one day the Valyrians netted and butchered one of the giant turtles the Rhoynar held sacred. As a result, thousands were killed or enslaved, cities and towns were burned, drowned and rebuilt. In these wars, the Valyrians emerged as victorious more often than not. The princes of the Rhoynish cities, fiercely proud of their independence, fought alone, whilst the Valyrian colonies aided one another.
Eventually, the Rhoynish princes ceased their squabbling and united behind Prince Garin, who led the largest army Essos had ever seen against 100,000 Valyrian colonists, 100 war elephants and three dragonlords. Thousands burned, but thousands more sheltered in the shallows of the river whilst the Rhoynish wizards raised enormous water spouts against the foes' dragons. Rhoynish archers brought down two of the dragons whilst the third fled wounded and thereafter the Rhoynar named Garin "the Great".
But Mother Valyria proved just as caring as Mother Rhoyne. When Garin the Great marched his army against Volantis, three hundred Valyrian dragons descended from the sky. Tens of thousands burned whilst others rushed into the river. But the fired burned so hot that the waters boiled and turned to steam. Garin the Great was captured alive and made to watch as Valyrians butchered every last man. SO many that their blood turned the great harbor of Volantis red as far as the eye could see. Then they forced Garin to watch as they marched on his own city and enslaved all the women and children his army had left behind. The singers claimed that Prince Garin called out Mother Rhoyne to curse the Valyrians, and she in turn flooded the city with foul waters and a damp fog that caused the skin of the Valyrians to harden and crack, and thus was born greyscale.
Fearing a similar fate, another Rhoynish ruler, Princess Nymeria, led her own people into every ship, skiff and raft they had and fled Essos. Eventually, after much hardship, they landed in sunswept and bone dry Dorne. But we all know that tale. Now Valyria has followed the Rhoynar out of this world and her daughters have grown into Free Cities, wealthy and powerful and proud. Still Mother Rhoyne flows on, past ancient ruins and bustling harbors, sweeping all man's kingdoms to the sea.