The Sanguinaires archipelago consists of four islets of dark red porphyry at the entrance to the Gulf of Ajaccio . They are called Mezu Mare (or Great Sanguinaire), Cormorans (or Isolotto), Cala d'Alga (30 m ) and Porri (31 m high). To this must be added the bare rock U Sbiru located between the isola di Porri and the island of Cormorans, at 13 m high .