St. James was the brother of John, and the first of the Apostolic College to suffer martyrdom. He was beheaded by Herod Agrippa about the year 43. He was one of the intimate friends of Our Savior: he witnessed the
Transfiguration and the agony in the Garden of Olives. Christ foretold his martyrdom on the occasion when the mother of James and John asked for her two sons that they be seated one at his right hand and the other at his left in His Kingdom. James preached the Gospel in Judea and Samaria, and even in distant Spain.
In the Sixth Century the tomb of the two apostles of the name of James was still being venerated at Jerusalem. But in the Ninth Century we find that the relics of St. James the Great were already the object of great devotion at Santiago de Compostella, whither they must have been carried after the Arabs had taken possession of the Holy City. Throughout the Middle Ages, the pilgrimage to Galicia to the tomb of St. James was on of the most popular of all, and wholly worthy of the special place which St. James occupied beside Our Blessed Lord.
(Source: The New Roman Missal, Rev. F. X. Lasance)