Porto Ercole occupies an inlet entered between the NE extremity of Colle della Rocca, on which stands Forte La Rocca, and Punta Santa Caterina 450 m N. Another hill, Monte San Filippo, 450 m W of Punta Santa Caterina, and on which stands Forte Fillipo, when viewed from the E, has a similar rounded appearance to Colle della Rocca.