As Italian was until 1848 the administrative language of Corsica, the town was originally named Isola Rossa (Red Island) from the eponymous reddish color of a rocky islet that served as a natural harbor.

Destroyed by the Phoenician fleet of Calaris (Galeria), Agilla came under Roman rule as Rubico Rocega (red rock) until the 4th century AD.

His plans prepared, he persuaded the Balagne government, sitting in Algajola, to authorize him to create a fort protecting the port (the Scalu) on 10 December 1765.

Built on a bay bounded to the northwest by the rocky islets of red porphyry which give it its name, and to the south by an immaculate white sand beach, l’Île-Rousse is presented to the tourist in all its beauty, extending westwards from the sea to the hill of the Sémaphore and the col de Fogata.

The old town of Pascal Paoli, le Père de la Patrie (the Father of the Fatherland), is made up of paved streets, almost rectilinear and oriented north-south.