Some of the earliest evidence found so far of human presence in the Aegean area, dating from c. 10,000 bc, has been unearthed in the ‘Cave of the Cyclops’ on the island of Gioura to the northeast of Alonnisos: and the earliest organised Neolithic settlements have been explored around the Bay of Aghios Petros on Kyra Panaghia, and at Kokkinokastro on Alonnisos. The island was later settled by pre Greek peoples, Carians and Dolopians. In historic times Alonnisos—called Ikos throughout Classical Antiquity— was, like Skiathos and Skopelos, a 7th century bc colony of Chalcis on Euboea. The 6th century bc writer and explorer, Scylax of Caryanda, mentions there being two cities on the island. The range in productivity of the Sporades islands can be seen in the fact that Ikos, as a member of the First Athenian League from 478 bc, was assessed at 1,500 drachmae in annual tithe, as opposed to 1,000 drachmae for Skiathos, and 18,000 drachmae (3 talents) for Peparethos (Skopelos). Having been allies of Athens in the Peloponnesian War, the Northern Sporades were subsequently occupied by Sparta. Ikos regained independence and was a member of the 2nd Athenian League until its dissolution in 346 bc. In 355 bc the neighbouring island of Halonnesos (probably to be identified as ancient Kyra Panaghia) was occupied by the pirate Sostrates; he was later expelled by the Macedonians, who built a fort on the island in 343 bc. Halonnesos became a bone of contention between Philip II of Macedon and the Athenians, and the issue is the subject of one of the orations of Demosthenes (Or. VII). In the settlement following the Battle of Chaeronea in 338 bc the Sporades along with Northern Greece fell under Macedonian supremacy. The island of Ikos, along with Skiathos and Skopelos, was devastated by Philip V of Macedon in 220 bc in his attempt to render them of no strategic use to his adversaries the Romans, who nonetheless became masters of the region after 146 bc. Mark Anthony later ceded the is lands to Athens in gratitude for the city’s military support.
Christianity must have come to the island around the time of the martyrdom of St Reginus on Skopelos in 362/3 ad, but the island was even more exposed than most to the destructive Slav and Arab incursions into the Aegean during the 7th and 8th centuries. In 1204, after the 4th Crusade, the island now apparently called ‘Chelidromia’, came under the possession of the Venetian Ghisi family together with the other Sporades islands. In 1276 they were driven out by the Veronese admiral Licario, acting on behalf of Constantinople, and the island was returned to Byzantine control up until 1453. After the fall of Constantinople the inhabitants sought the protection of the Venetian Republic, which subsequently governed the island, except for a decade of Turkish occupation between 1475 and 1486, until 1538 when it was ransacked and finally captured for the Turks by Khaireddin Barbarossa. During the following centuries the outer islands of the Sporades suffered particularly from piracy; but they enjoyed tax privileges bestowed by Osman III in 1756. In 1821, in the course of the Greek War of Independence, a free ‘Demos Alonnisou’ under the jurisdiction of the new Greek administration of the Sporades was declared. The island was officially ceded to the Greek State by Turkey in 1830.
In 1965 the island’s main centre of population at Chora was badly damaged by a severe earthquake; the population was moved to Patitiri, in the area of the harbour. In May 1992, the ‘National Marine Park of Alonissos Northern Sporades’ (NMPANS) was established by Presidential decree to protect the landscape and waters of the area, and the habitats of rare and threatened species of plant and animal—most especially the Mediterranean monk seal (Monachus monachus). In 1994 George Vithoulkas established the centre of the International Academy of Classical Homeopathy on Alonnisos.
Alonnisos Island is part of the Sporades Island Group, Greece.