Whisk together the flour, salt, sugar, and yeast in a large bowl. Add the water and mix until a shaggy mixture forms. Cover the bowl with plastic wrap and let sit at room temperature for 12 to 18 hours. (After sitting, the dough will be sticky and sponge-like.)
Preheat oven to 450F. When the oven is hot, place a cast iron pot with a lid in the oven and heat the pot for 30 minutes. Meanwhile, pour the dough onto a very heavily floured surface, flour your hands, and shape into a ball (without kneading), adding more flour as necessary so the dough holds its shape without expanding too much. Cover with plastic wrap and let it rise until puffed, about 30 to 45 minutes.
Remove the hot pot from the oven and drop in the dough. Cut 3 slashes across the top of the dough with a sharp knife. Cover and return to oven for 30 minutes. After 30 minutes, remove the lid and bake an additional 15 minutes.
Remove bread from the pot and place on a cooling rack to cool.