In antiquity the island was called Keria.
The first mention of this is found on an inscription bearing the names of the taxed city states that belonged in the alliance of the Athenian democracy.
It’s area is estimated to be 15,042 squ km and the length of its coastline 27 km.
On the island there is no trace of drinkable water and access is not easy.
A characteristic feature is the white marble.
Keros is a protected archaeological site and an important source of archaeological finds, which complement a large part of the Cycladic civilization.
On Keros two very important statuettes of the early Cycladic civilization were discovered, those of the Flute Player (Avlitis) and Harp Player (Arpistis), which are now exhibited in the Athens Archaeological Museum and are important in the study of the religious life of the people of that period.
In the Middle Ages the island was used as a pirate hideout, while up until 1952 it belonged to the monastery of the Holy Virgin Hozoviotissa of Amorgos.
On the islet across, Kavos Daskaliou, there have been found a large number of archaeological finds and Cycladic statuettes which lead archaeologists to speculate that the island was a centre of worship during the early Cycladic era, on a similar scale as Apollo’s temple on Delos.
At Daskalio there has also been found a considerable fortified settlement dating from the same time.
Due to its archaeological wealth, Keros has often been plundered by antique smugglers.
This is where the Treasure of Keros comes from, which used to belong to the Erlenmeyer collection, whereas nowadays its greatest part is in the Museum of Cycladic Art.
The island was systematically excavated by the Archaeological Department in 1963 and 1967.
Some finds from Keros can be seen in the Museum of Naxos.
In the 2000s, a team under Professor Colin Renfrew brought a host of finds to light.
A rare experience for visitors to Koufonissi is on full moon nights when Keros looks like the outline of a couple lying down. The woman, pregnant, lying with her figure perfectly outlined, head to head with the man whose profile is clearly discernible.
These days Keros is uninhabited and access is forbidden due to the archaeological excavations that still continue from time to time.
According to the locals, the energy emanating from this island creates the atmosphere of peace and positive emotion that Koufonissi gives off.