I stood and looked in the cool of the twilight -
the sun was peacefully sinking low,
her last rays glowing and lovingly encompassing
the world in a soft and rich, warm glow.

Suddenly a trembling, rumbling, grumbling
shook the world of that mighty plain.
and out of the east, with a powerful thundering,
the wild black horses of dark night came,

Tossing their heads as they galloped in number,
their tails outstretched in the whistling wind.
I stood transfixed as they surged towards me,
unable to move or turn away.

Larger and larger they grew and larger,
until in their race they surrounded me.
With thrashing hooves in their furious charge,
they rushed right on to the western sea.

Until they reached those deep, deep waters,
and left me behind in the night - alone.

(1961)

Diana van den Berg

http://www.poemhunter.com/poem/wall-of-darkness/