Without them, there probably wouldn't have been any shrines, and without the shrines there wouldn't have been any pilgrims, and without a body in a reliquary casket in Santiago de Compostela, there wouldn't have been any pilgrims or a camino pilgrimage. Luckily for us, relics became popular from about the 5th C and by the time of Charlemagne (8thC) no church could be consecrated without a relic.
“... we honor the martyrs' relics, so that thereby we give honor to Him Whose [witness] they are: we honor the servants, that the honor shown to them may reflect on their Master... Consequently, by honoring the martyrs' relics we do not fall into the error of the Gentiles, who gave the worship of "latria" to dead men."
What can the modern pilgrims to
Here is a list of some of the relics still to be found in the churches of
Not on the camino, but a very important relic in Spain. In the Monastery of Santo Toribio of Liébana there is the relic of the Lignum Crucis, the largest surviving fragment of Christ’s Cross.