The Rohirrim, why horses?

[Bêthberry]

Tom Shippey's Road to Middle-earth does indeed posit an explanation for the presence of horses in The Mark.

Shippey argues that Tolkien is 'calquing' (a word from Tolkien's professional study of philology).

Originally Posted by Shippey

A part of the answer is that the Rohirrim are not to be equated with the Anglo-Saxons of history, but with those of poetry, or legend.

At some length Shippey discusses the similarities between "The King of the Golden Hall" and the Old English poem Beowulf, to say nothing of the similarities between Aragon's song and the Old English poem The Wanderer.

Originally Posted by Shippey

However, Tolkien was trying to go beyond translation to 'reconstruction.' And this is what explains the horses. The feeling of Anglo-Saxon poetry for these was markedly different from that of Anglo-Saxon history. Thus the retainers of Beowulf joyfully race their mearas back from the monsters' lake as they singe their praise songs. . . . Maybe the infantry-fixation of historical periods was the result of living on an island. Maybe the Anglo-Saxons before they migrated to England were different. What would have happened had they turned East, not West, to the German plains and the steppes beyond?

It's a fascinating argument in part because it employs the same technique that Tolkien employed to develop his languages.