The triple spiral is found in artefacts of the European Neolithic and Bronze Age with continuation into the Iron Age especially in the context of the La Tène culture and related Celtic traditions. The actual triskeles symbol of three human legs is found especially in Greek antiquity, beginning in archaic pottery, and continued in coinage of the classical period.
In the Hellenistic period, the symbol becomes associated with the island of Sicily, later appears in heraldry, and came to be used in the flag of the Isle of Man- from wikipedia.