The original population of Cornwall was probably Iberic, of the same primitive race as the dark-haired population of Ireland, before the island was invaded and subjugated by the Celts.
The branch of the Celts in Britain and Cornwall was Brythonic, and there is nothing certain to show that the Goidels were in Cornwall before the Brythons. It is true that some few river names, and again inscriptions are Irish, but these latter pertain to the settlement in Cornwall of Irish expelled from Ossory and Wicklow in the fifth century.
Popularly the dark hair and dusky complexions of some of the Cornish is attributed to Spaniards wrecked from the Armada. But no Spanish wreck came on shore in Cornwall. The first loss the Armada sustained was east of Plymouth. On its way back to Spain none of the vessels came near Cornwall. Several were wrecked on the coast of Ireland and their crews massacred to a man by the natives.
Posidonius travelled after B.C. 123 and visited Spain, where he collected a variety of information on points of geography and natural history, and after spending thirty days at Gades returned to Italy. He learned among other things something about the collection of tin in Bolerium, a name afterwards appropriated by Ptolemy to the Land's End. He says: "The inhabitants of that promontory of Britain which is called Bolerium are very fond of strangers, and from their intercourse with foreign merchants are civilised in their manner of life. They prepare the tin, working very skilfully the earth in which it is produced. The ground is rocky, but it contains earthy veins, the produce of which is ground down, smelted, and purified. They make the metal up into slabs shaped like knuckle-bones, and carry it to a certain island lying in front of Britain called Ictis. During the ebb of the tide the intervening space is left dry, and to this place they carry over abundance of tin in their waggons.... Here then, the merchants buy the tin from the natives, and carry it over to Gaul; and after travelling overland for about thirty days, they finally bring their loads on pack-horses to the outlet of the Rhone." It is very doubtful whether Posidonius ever visited Britain. What he relates is doubtless due to information received by him, either at Gades or at Massilia.