Passé simple

The passé simple, translated in English as either "simple past" or "preterite," is the literary equivalent of the passé composé, which means that it is used only in formal writing (e.g., historical and literary writing) and very formal speech.

In such writing and speech, the passé simple is used alongside the imperfect, just as in everyday speech/writing, the passé composé and imperfect are used together.

The passé simple (past definite) is used primarily in formal, literary, and historical writings to express a completed past action, event, or situation. In conversation and informal writing, the passé composé is used instead of the passé simple to express the past


In modern spoken French, the passé simple has practically disappeared


While literary and refined language still hangs on to the passé simple, the spoken language has simply renounced passé simple for the passe composé, which means that in French, there is no longer a nuance between:
« Je suis arrivé. » ("I have arrived." I have come to town. I may have just arrived.)
« J'arrivai. » ("I arrived." I came to town, but it is possible that I am not still here.)


References
http://french.about.com/od/grammar/a/passesimple.htm
http://en.wikipedia.org/wiki/Pass%C3%A9_simple
https://facultystaff.richmond.edu/~jbaker/passesimple.html