The island of Alonissos was one of the first inhabited islands of Greece. In Greek mythology it was the home of Stafylos ("Grape") who was the son of Ariadne and Dionysus (god of wine). In ancient times the island was called Ikos. Then after the independence war against Turkey all islands were given a Greek name again, the island was accidentally assigned the name of Alonissos. Alonissos was actually the name of what is now the island of Kyra Panagia. Alonissos means something like "island that comes up out of the sea". The Greek "alt" meaning "salt" and nissos means "island". The many shipwrecks dating from the classical and Byzantine period that have been found around the island show that the Alonissos was a major economic power.

At the beach of Kokkinokastro lie the remains of the ancient city of Ikos and its burial grounds in the sea. During the Mesolithic period (10000-5000 BC) it was already already here. Even tools from the Old Stone Age have been found. During the classical period (around 500 BC) a wall was built around the city for protection. Those who go snorkeling at Kokkinokastro can still see the remains of this wall in the sea. Tombs and pottery shards have also been found. It is not recommended to go climb the headland from the beach to have a look around because it is dangerous. It is thought that one of the tombs in Kokkinokastro / Ikos is of King Peleus, the father of Achilles.

In the classical period, there were two towns on the island. There was Ikos and the other city stood on the spot where now the Chora is situated. There were many vineyards and wine exports was the main source of income for Alonissos. The island was prosperous and there was lot of trade. On the amphorae of the island the name "Ikion" was inscribed. In the vicinity of Alonissos many shipwrecks have been discovered testifying that the island was on an important sea route.

Behind the beach of Tsoukalia and in the sea in front of it many potsherds have been found, sometimes bearing the name "Ikion". In the classical period, around 400 BC, there were ovens here where the amphorae were made in which the wine and olive oil of Alonissos was transported. The area behind the beach is now a protected archaeological site. The name Tsoukalia in Greek means "pots". In the beginning of the twentieth century the area behind Tsoukalia Beach was again used for making pots.

At the bottom of the sea in front of the beach of Marpounta the remnants have been found of a temple that was likely dedicated to Aesculapius or Asclepius, the god of medicine, who in Greek mythology was the son of Apollo and Coronis. Today thhe best preserved sanctuary that is dedicated to this god can be found on the island of Kos.

At various places there are remnants of churches from the Byzantine period, including a basilica just behind the beach of Agios Dimitrios, and churches near Agios Petros Beach and at Agios Andreas. The beach of Agios Dimitrios takes its name from a monastery that dates from the Byzantine times. It was situated here just above the beach, and it was destroyed by pirates. The remains of a wall and a basilica can still be seen near the main road that runs across the island. Just behind the beach is an area of wetlands where migratory birds make a stop. In the summer this area is dried out.

Scattered across the island the remains of settlements and watchtowers have been uncovered. In Agios Yiannis they found an observatory on a hill and a small settlement from the classical period, with a tower that gave views over the island of Alonissos and the strait between Alonissos and the neighboring island of Peristera. In Steni Vala ancient buildings and potsherds have been found. In Garbitsa are the remains of a tower that overlooked the area south of the island, and in Kastraki a fortress with a tower was uncoverd.

In the Chora there are 3 Byzantine churches and the remains of the Venetian fortress.

In the west of the island at the end of an unpaved road between Megali Ammos and Tsoukalia Beach you find the monastery / Byzantine church of Agioi Anargyroi (the Saints of Anargyroi). Next to the remains of the old monastery a new church has been built. The ancient Byzantine church is quite small and looks more like a house made of stone with a dome on top. It dates from the 13th century. In the extreme north of the island there is the monastery of Analipsi. I have no further information, and do not know if you can reach this monastery on foot from the beach of Gerakas.