Warwick Deeping 
The Seven Streams [PDF ebook] 

Tristan le Sauvage left the Purple Isle upon a knightly quest—to recover his sister from The Land of Seven Streams. Two months had passed since a great ship, with gleaming sails, had swooped like a falcon upon Purple Isle, and carried thence that white dove, Columbe the Fair. In the Land of Seven Streams, Tristan finds many other knightly services in the struggle between papacy and people, and again, between the broken ranks of the Christians and the Saracen hordes. 
The book is a charming romance, where Deeping simulates a historical realism by depicting Arthur’s world not as the chivalrous court of the late Middle Ages as found in Malory (followed by Tennyson and most nineteenth-century poets), but as the more appropriately rugged tribal society of the sixth century. Yet even this seeming realism soon yields romance, for the world of Deeping’s novels depicts Roman elegance more than the crude realities of Saxon invasions and Briton resistance.