Sifnos was inhabited by human beings from at least 4000 BCE. Archeological evidence indicates the island was within the mainstream of Late Neolithic and Early Bronze Age Cycladic civilization. The island was very wealthy in ancient times, thanks to its gold, silver, and lead, which were being mined there as early as the 3rd millennium BCE. Proof of this is the treasury which the Siphnians built at Delphi in the 6th century BCE to house their offerings. According to Pausanias, these mines were obliterated by floods in ancient times, a disaster which some attributed to the people of the island suspending their tribute out of greed. Modern scholars suggest that some of the mines flooded because they had eventually been dug to a depth below sea level, while the majority of them, situated far from the sea, were probably exhausted. Remains of ancient mines, some dating back to prehistoric times, are still to be seen on the island, most notably at Ay. Sostis, and remains of ancient fortifications, dating from the third millennium to the sixth century BCE, have been found at Ay. Andreas, Ay. Nikitas, and Kastro. Another indication of Sifnos's wealth is the fact that it was one of the first places in Greece to mint coins, beginning around 600 BCE, although the number minted does not seem to have been great, and the island of Aegina, which used Siphnian silver, seems to have developed a much greater export capacity in this form of the metal.
During the extensive Greek migrations which occurred beginning perhaps as early as the 12th century BCE, Sifnos was mostly populated by Ionian Greeks from Athens. The island appears only rarely in the subsequent ancient history of Greece. In the sixth century BCE it was invaded by pirates from Samos. In the fifth century BCE, Sifnos was an official member of the Greek defensive alliance formed to fight the Persian Wars. In the next century the island was briefly taken over by the Persians but liberated by a fleet sent by Alexander