Once, a mighty river ran south into the sea -- and at the mouth thereof rose a great and rich city, which had been builded and had waxed and thriven because of the great and excellent haven which the river made, there where it flowed into the sea. It was like looking at a huge wood of barked and smoothened fir-trees, when one saw the masts of the ships that lay in this haven.

And up this river ran the flood of the tide -- and it ran a long way up, so far that the biggest of round-ships might fare up its course . . .

So begins The Sundering Flood, a fantasy first published just after the death of its author.