The croissant was actually invented in Vienne, to celebrate the defeat of the Turks in 1683 (or it might have been 1529, who knows, the Turks were always beseiging the place). In France, this sort of pastries are called Viennoiserie. SO, ALTHOUGH THE STANDARD BREAD LOAF IS A pAIN pARISIEN, THE CROISSANT IS REALLY NOT pARISIAN.
Anyway, what is a croissant? it is a roll of flaky pastry made with bread dough. This presents special problems, because anybody who has made flaky pastry will tell you that it meeds to bekept COOL, while the raising agent in bread dough is yeast, which has to be WARM. French bakers, with centuries of practice, manage to reconsile these differences, but amateurs who try the job make an awful mess. Either the butter between the layers melts, or the yeast deactivates.
Once the basic pastry is made - layer upon layer of thinly-rolled dough alternating with layers of butter - it is cut into isosceles triangles and rolled up from the base, ending with the apex. the two ends can then be curled round to make horns, and the finished article ca look just a bit like the crescent on the Turkish flag. Into a hot oven with it, and with luck it will expand and become crisp on the outside and indescribably delicious on the inside.
WARNING: if you have never been to France, you have never tasted a croissant. Evry French baker can make them, and nobody else. Vienna? Don't make me laugh. I don't think the Viennese croissant was ever flaky, anyway.