Third millennium BCE (First Cycladic Period) findings at Skouries near the highest peak of the island, Mt. Profitis Elias, suggest that Kythnos was a supplier of raw materials for metallurgy to other islands during the Bronze Age.
Remains of copper smelting sites and open-air copper mines were investigated in 1984–1985. (
A recent paper by Myrto Georgakopoulo points to the seminal work here by Gale and others.)

The earliest inhabitants of the island known to historians were the Kares (Carians), a pre-Hellenic tribe probably allied to or under the dominion of the Minoans, who eventually were forced by pressure of invading tribes to move on and settle in Asia Minor.
Herodotus (Bk.
viii, 73) records that in the 13th century BCE, another pre-Hellenic tribe, the Dryopes, originally from the Greek mainland near Mount Parnassus, migrated to the islands, first to Euboea and later spreading to Kea, Kythnos, and beyond.
This tribe most probably gave rise to the name of one of the two main villages, Dryopis or Dryopida.
Some sources say the island took its name from King Kythnos of the Dryopes; others suggest this is a mythical rather than a historical figure. (
Speculations on the origin of the name are contained in Vallinda, 1896.)
The Dryopes eventually moved on as well under pressure from Ionians, who migrated out of mainland Greece as Dorian tribes moved in from the north.

A Hellenistic site at Vryokastro, above the bay of Episkopi on the northwest part of the island, was partially excavated in the mid-20th century, yielding floor plans of houses and a sanctuary, as well as a few artifacts.
In Greek newspaper articles of December 19, 2002, archaeologist Alexandros Mazarakis-Ainian announced a spectacular discovery on this site: an inner sanctum (adyton) of the temple was found intact and unplundered.
Over 1,400 objects, including precious jewels and gold, silver and bronze artifacts, terracotta figurines, and painted vases, were excavated from what the archaeologists have determined is a 2,700-year-old temple dedicated to either Hera, queen of the gods, or Aphrodite, goddess of love.
The artifacts date mostly from the 7th to the 5th centuries BCE.
The site at Vryokastro was inhabited until Roman times.
In this era, the islands of the Cyclades suffered frequent predation by pirates, and perhaps for this reason, the main settlements moved inland and to more defensible locations.

Remains of another old settlement, with extensive stone walls, can be seen in the extreme northern headland.
This site, called Kastro (Greek for Castle), was likely the capital of the island from about the 1st century through the Byzantine era and into Frankish times.
This site seems nearly impregnable: on three sides is a sheer 500-foot (150 m) drop to the sea.
The fourth side is approached via a narrow track, which was barricaded with a thick, high wall, parts of which are still extant (along with walls delineating hundreds of houses).
Nevertheless, there is evidence that the town was destroyed and rebuilt several times.
The population fluctuated dramatically during this period and at times the island was decimated due to marauders and plague (Smith, 1854 and Bent, 1885, reprinted 2002).
Third millennium BCE (First Cycladic Period) findings at Skouries near the highest peak of the island, Mt. Profitis Elias, suggest that Kythnos was a supplier of raw materials for metallurgy to other islands during the Bronze Age. Remains of copper smelting sites and open-air copper mines were investigated in 1984–1985. (A recent paper by Myrto Georgakopoulo points to the seminal work here by Gale and others.)
The earliest inhabitants of the island known to historians were the Kares (Carians), a pre-Hellenic tribe probably allied to or under the dominion of the Minoans, who eventually were forced by pressure of invading tribes to move on and settle in Asia Minor. Herodotus (Bk. viii, 73) records that in the 13th century BCE, another pre-Hellenic tribe, the Dryopes, originally from the Greek mainland near Mount Parnassus, migrated to the islands, first to Euboea and later spreading to Kea, Kythnos, and beyond. This tribe most probably gave rise to the name of one of the two main villages, Dryopis or Dryopida. Some sources say the island took its name from King Kythnos of the Dryopes; others suggest this is a mythical rather than a historical figure. (Speculations on the origin of the name are contained in Vallinda, 1896.) The Dryopes eventually moved on as well under pressure from Ionians, who migrated out of mainland Greece as Dorian tribes moved in from the north.
A Hellenistic site at Vryokastro, above the bay of Episkopi on the northwest part of the island, was partially excavated in the mid-20th century, yielding floor plans of houses and a sanctuary, as well as a few artifacts. In Greek newspaper articles of December 19, 2002, archaeologist Alexandros Mazarakis-Ainian announced a spectacular discovery on this site: an inner sanctum (adyton) of the temple was found intact and unplundered. Over 1,400 objects, including precious jewels and gold, silver and bronze artifacts, terracotta figurines, and painted vases, were excavated from what the archaeologists have determined is a 2,700-year-old temple dedicated to either Hera, queen of the gods, or Aphrodite, goddess of love. The artifacts date mostly from the 7th to the 5th centuries BCE. The site at Vryokastro was inhabited until Roman times. In this era, the islands of the Cyclades suffered frequent predation by pirates, and perhaps for this reason, the main settlements moved inland and to more defensible locations.
Remains of another old settlement, with extensive stone walls, can be seen in the extreme northern headland. This site, called Kastro (Greek for Castle), was likely the capital of the island from about the 1st century through the Byzantine era and into Frankish times. This site seems nearly impregnable: on three sides is a sheer 500-foot (150 m) drop to the sea. The fourth side is approached via a narrow track, which was barricaded with a thick, high wall, parts of which are still extant (along with walls delineating hundreds of houses). Nevertheless, there is evidence that the town was destroyed and rebuilt several times. The population fluctuated dramatically during this period and at times the island was decimated due to marauders and plague (Smith, 1854 and Bent, 1885, reprinted 2002).
Kythnos