From John Le Carré's Smiley's People:
Lacon, Strickland, Mostyn, thought Smiley as Strickland’s Aberdonian brogue hammered on. One Cabinet Office factotum, one Circus fixer, one scared boy. Why not real people? Why not Vladimir’s case officer, whoever he is? Why not Saul Enderby, their Chief?
A verse of Auden’s rang in his mind from the days when he was Mostyn’s age: Let us honour if we can/The vertical man/ Though we value none/But the horizontal one. Or something.
And why Smiley? he thought. Above all, why me? Of all people, when as far as they’re concerned I’m deader than old Vladimir.
What do "the vertical man" and "the horizontal one" quoted from Auden's verse mean here? Does the former refer to the living and the latter the dead?