In "The Horses," the title animals represent the forces of nature and man's inability to fully comprehend their purpose. They stand throughout the night, waiting for dawn, and the narrator is in awe of their stillness:

Huge in the dense grey – ten together –
Megalith-still. They breathed, making no move,

With draped manes and tilted hind-hooves,
Making no sound.

I passed: not one snorted or jerked its head.
Grey silent fragments
Of a grey still world.

His appreciation of the horses changes almost to fright as dawn breaks, and the horses remain still as the frost steams off them. He then recounts the effect the experience had on him:

In din of the crowded streets, going among the years, the faces,
May I still meet my memory in so lonely a place

Between the streams and the red clouds, hearing curlews,
Hearing the horizons endure.
(Quotes: Hughes, "The Horses," jeanettewinterson.com)

His comparison of the horses to "megaliths" is a clue to the last line's meaning; the horses are as natural as the horizon itself. They both remain and endure whatever comes their way with stoic patience, and have little concern for what goes on outside their realm. The narrator feels a connection to that "lonely place" while "in din of the crowded streets," and just as he could hear and feel the horses in their natural place, he can "hear" the horizons of the Earth endure throughout time and history.