Cathedrals and churches of the pilgrimage routes for Cathedral of Santiago de Compostela

The pilgrimages were at their culmination during the middle ages, especially in the eleventh and the twelfth century. The cathedral of Compostela became one of the three most important churches in the Christian world alongside the Holy Sepulcher in Jerusalem and the Tomb of St. Peter in Rome. Jerusalem is considered the oldest of these holy places, which is why at the beginning of the middle ages when the Christian religion has spread, Christians began to go on pilgrimages in the form of crusades; one after the other. This occurred after Muslims had invaded Jerusalem in the eighth century AD and destroyed the Holy Shrine.
As for St. Peter's cathedral, which contains the remains of Saints Peter and Paul, and the tombs of the early martyrs, the importance of its great pilgrimage in the Romanesque era decreased for a period of time due to repeated attacks from Germany on Rome in 1084. Consequently, the cathedral of Compostela in Galicia in northwestern Spain became the pilgrimage lighthouse during the Romanesque era. Also, the cathedral of Compostela has the remains of St. Yacoub Bin Zebedee, the apostle (known as St. James and also Santo. Iago), one of the disciples of the Christ, the patron of the poor and the protector saint of Spain.
Many monasteries, cathedrals, churches and dioceses flourished along the four pilgrimage routes in France and Spain: Tolosana, Podensis, Limovicensis, and Turonensis.
Research Problem: What is the importance the cathedral of Compostela and the importance of of St. Bin Zebedee? Are there cathedrals and churches on the four pilgrimage routes leading to this cathedral and each of them represents a pilgrimage church in itself? Do the general features of their architecture and arts differ between them? Does religion affect the architectural formulations of houses of worship?