In a colander rinse olives under cold water 1 minute and in a large bowl cover with cold water. Soak olives 4 hours to remove excess salt and drain well.
To make the harissa: In a mortar with a pestle, an electric spice grinder, or a cleaned coffee grinder, grind seeds fine. If using mortar and pestle, add chiles, garlic, and salt and pound, to taste. If using a spice or coffee grinder, transfer seeds to a small food processor and add chiles, garlic, and salt. Grind mixture to a paste. Add pepper and oil and pound or puree to a coarse paste.
In a large bowl stir together the harissa and olives and marinate, covered and chilled, at least 6 hours or overnight. Olives may be prepared 1 week ahead and kept chilled, covered.
Serve olives at room temperature.
Roasted Peppers: Using a long-handled fork, char peppers over an open flame or on a rack set over an electric burner, turning, until skins are blackened, 4 to 6 minutes. (Or to broil peppers on rack of a broiler pan under a preheated broiler about 2 inches from heat, turning every 5 minutes, 15 to 20 minutes, or until skins are blistered and charred.) Transfer peppers to a bowl and let stand, covered, until cool enough to handle. Keeping peppers whole, peel them, starting at blossom end. Cut off pepper tops and discard seeds and ribs.