In a large bowl, stir together the flour, salt, yeast, and rosemary. Add the water a little at a time, scraping down the sides of the bowl.
When the dough has just come together, turn it out onto a lightly floured surface and knead the ball until the dough is smooth, about 10 times. Then return the dough ball to the bowl. Cover with a damp towel, and allow to rest in a warm place for at least 6 hours, or overnight.
When the dough has rested, it will have risen to double its size. Move the dough to a floured durface again and knead again. Let it rest, covered, for one more hour.
Place the dutch oven in the your oven and preheat the oven to 450°F.
Take the dutch oven out of the oven (it will be hot!) Coat the dough ball with a thin layer of olive oil and place the dough in the pot. Cover the dutch oven and bake for 30 minutes. Uncover and bake an additional 15 minutes.
Remove the dutch oven from the oven and allow the bread to rest in the dutch oven for 5 minutes before removing it. Allow to cool on a room temperature surface for at least ten minutes before slicing.