Soak the dried chillis in tepid water to cover until softened, about 45 minutes to 1 hour.
Drain and remove the stems and seeds.
Place in a blender or food processor with the garlic, water, and olive oil and process until smooth, stopping occasionally to scrape down the sides.
Transfer the mixture to a small bowl and stir in the caraway, coriander, and salt.
Store in a jar and top off, covering the surface of the paste with a layer of olive oil.
Whenever the paste is used you must always top off with olive oil making sure no paste is exposed to air otherwise it will spoil.
Variation: To make a hot harisa, use 4 ounces dried guajillo chillis and 1/ 2 ounce dried de Arbol chillis.
Note: To make salsa al-harisa, that is, harisa sauce, used as an accompaniment to grilled meats, stir together 2 teaspoons harisa, 3 tablespoons olive oil, 2 tablespoons water and 1 tablespoon finely chopped fresh parsley leaves.