42°34′56″N 10°04′42″E / 42.58222°N 10.07833°E / 42.58222; 10.07833

Pianosa (Italian pronunciation: [pjaˈnoːza]) is an island in the Tuscan Archipelago in the Tyrrhenian Sea, Italy. It is about 10.25 km² (3.96 sq mi) in area, with a coastal perimeter of 26 km (16 mi).

In Roman times, the island was named Planasia (plain) because of its flatness – its highest point stands at 29 m (95 ft) above sea level. It is a triangular-shaped land mass 14 km (9 mi) south-west of Elba and is a frazione of the municipality of Campo nell'Elba. Pianosa is the fifth biggest island of the Tuscan Archipelago and the only one to be formed out of sedimentary rock of the Neogene and Quaternary; such fossils as echinoderms, mollusca and bryozoa of the Pliocene are frequently found.

The vegetation consists mainly of Mediterranean species as lentisco, fennel, juniper, rosemary and Pinus halepensis, which was introduced on the island in the 1900s.

The animals living on the island are largely small mammals, such as hedgehog and hare, introduced in the 1800s, as well as the pheasant and the red-legged partridge; the magpie and the Audouin's gull nest along the coast and are protected by the National Park. The island is a stopping place for migrating birds in their seasonal passage from North to South. The sea around Pianosa is rich in fish because the coast was unapproachable for a long time, while today National Park regulations forbid fishing. Grouper, dory, dentex, moray, crawfish and many other species of fish inhabit the seas around the island.

The island was first inhabited in the Upper Palaeolithic, the Later Stone Age, but when in 5000 BC the sea level rose and reached the current level, the few inhabitants took refuge on the nearby Scola islet, where traces of their presence were found. Fishing tools and ceramics of the Mesolithic were found, as well as artefacts in quartz and flint, probably coming from Elba. The ancient Romans' Planasia had structures and was extensively cultivated. It became noted in history when the princeps Augustus banished his grandson and former designated heir Agrippa Postumus there in 6 or 7 AD. Postumus remained there until his murder by an assassin sent by Tiberius, around 14 AD. Postumus lived in Pianosa at Villa Agrippa, which was discovered by abbot Gaetano Chierici in the second half of 1800s and included a theatre, a thermal bath (Bagni di Agrippa), and a Roman villa with black and white mosaic floors with marine-themed mythological decorations.

In the 4th century, a small Christian community lived in Pianosa and left traces of their presence in catacombs. These are on two levels and are the largest north of Rome; 700 catacombs were discovered, indicating a fair number of residents.

Pisa had custody of the island after a nearby naval battle victory in 874. In the Middle Ages the island's ownership was disputed by Pisa and Genoa because of its strategic position. In 1238, Genoa sent troops to the island with the pretence that the inhabitants engaged in piracy. The troops destroyed the village and the fortifications built by the Pisans and took the 150 inhabitants prisoner. Pianosa was returned shortly afterward to Pisa, but Genoa had the supremacy of the Tyrrhenian Sea after the Battle of Meloria. The island returned to Pisan control under an agreement that required the Pisans to leave it uncultivated and uninhabited, but the pact was not honoured. The Appiano family, who ruled Pisa, leased the island to the De Leis family and then to the Landi family in 1344. The Appianos sold Pisa to Gian Galeazzo Visconti in 1399 and established the small Principality of Piombino, which included Suvereto, Scarlino, Vignale, Populonia and the islands of Elba, Montecristo and Pianosa. On August 15, 1552, the Holy Roman Emperor Charles V of Spain consigned to Cosimo I de' Medici the Principality of Piombino in exchange of a loan of 200,000 scudi.