The Celtiberians are the people who inhabited parts of the Iberian
peninsula up until such time as they were conquered by the Romans. They
were mainly in the north and in the area now known as Portugal.
'The Book of Invasions' has at least one of the invasions of Ireland
coming from Spain.
One of the sixth century AD Councils of Toledo has a Bishop Mailoc who
signs himself as Bishop of the Britons, a bishopric in northern Spain
established by refugee Britons.
The works of Isidore of Seville, a seventh century Spanish writer, the
first encyclopedist of the Middle Ages, were known in Ireland before they
were known in other parts of western Europe. See, for this and other
contacts between early medieval Ireland and Spain, the papers by
J.N. Hillgarth, one of which was from the Journal 'Peritia' from the
early/mid eighties, and the others from 'Proceedings of the Royal Irish
Academy' in the sixties, all reprinted in her volume of reprinted journal
articles published by 'Variorum Reprints'.
In the late fifth and early sixth centuries Byzantine traders were coming
through the straits of Gibraltar on their way to the British Isles, they
came mainly to trade for Cornish Tin in return for eastern goods,
including the archaeologically identifiable fine table wares and
amphorae, some of which found its way to Ireland, mainly southern/eastern.
Classical geographers thought that Ireland lay between Gaul and Spain.
Hope these help.
Mark Handley, Trinity Hall, Cambridge.