Couches

 Probably you know how to leaven a dough in a basket or banneton, and you can expect your baked loaf to look something like this.

 However, if you are baking a baguette-style loaves, then you need to leaven them in couches.

 Use linen or cotton fabric to make your couches.

You might say, "why not just leaven them in gutter pans and bake the whole ensemble in the oven?" The reason you don't do this is because you want your breads to make intimate contact with the floor (hearth/deck) of the oven for superior loaves.