In a Station of the Metro -- Ezra Pound

(Poem #319) In a Station of the Metro The apparition of these faces in the crowd; Petals on a wet, black bough. -- Ezra Pound

Possibly the first true Imagist poem, and certainly one of the finest. I'll
 leave you to read Pound's own words about its composition:

"Three years ago in Paris I got out of a `metro' train at La Concorde, and
saw suddenly a beautiful face, and then another and another, and then a
beautiful child's face, and then another beautiful woman, and I tried all
that day to find words for what this had meant to me, and I could not find
any words that seemed to me worthy, or as lovely as that sudden emotion. And
that evening, as I went home along the Rue Raynouard, I was still trying,
and I found, suddenly, the expression. I do not mean that I found words, but
there came an equation... not in speech, but in little splotches of colour.
It was just that -- a  `pattern', or hardly a pattern, if by `pattern' you
mean something with a `repeat' in it. But it was a word, the beginning, for
me, of a language in colour. I do not mean that I was unfamiliar with the
kindergarten stories about colours being like tones in music. I think that
sort of thing is nonsense. If you try to make notes permanently correspond
with particular colour, it is like tying narrow meanings to symbols.

That evening, in the Rue Raynouard, I realized quite vividly that if I were
like a painter, or if I had, often, that kind of emotion, or even if I were
a painter, or if I had the energy to get paints and brushes and keep at it,
I might found a new school of painting, of `non-representative' painting, a
painting that would speak only by arrangements in colour... The `one image
poem' is a form of super-position, that is to say, it is one idea set on top
of another. I found it useful in getting out of the impasse in which I had
been left by my metro emotion. I wrote a thirty-line poem, and destroyed it
because it was what we called work `of second intensity.' Six months later I
made a poem half that length; a year later I made the following hokka-like
sentence [In a Station of the Metro]. I dare say it is meaningless unless
one has drifted into a certain vein of thought. In a poem of this sort one
is trying to record the precise instant when a thing outward and objective
transforms itself, or darts into a thing inward a subjective."

    -- Ezra Pound, quoted in A Guide to Ezra Pound's Personae (1926). K. K. Ruthven (1969).