an island in the Mediterranean, belonging to Tuscany, lies about 10 miles S.S.W. of Elba, and nearly 40 from the nearest point of the mainland. It is 3 miles long by 2½ broad, and is about 10 miles in circuit. The surface is low; but it is fertile and well wooded, and is chiefly inhabited by fishermen. In the island are granite quarries, probably worked in the time of the Romans, when it was called Planasia. It was here that Postumus Agrippa was banished by Augustus, and afterwards put to death by order of Tiberius. Pianosa was annexed to Elba and granted to Napoleon after his first abdication.