Christian writers, from the earliest years were keen to set down in writing the lives of the saints and the miracles which they performed, whether during their lifetime or through their relics after death. Many of these texts failed to survive the ravages of religious warfare and revolutionary zeal. At the cathedral of Santiago de Compostela
there exists in complete form the full twelfth century text of the cult which was venerated there.
The Liber Sancti Iacobi or the Book of Saint James is often referred to as the The Codex Calixtinus after Pope Calixtus II by whom it was purportedly written, although it is clearly derived from a number of sources. Scholars are agreed that it was written around the middle of the twelfth century and comprises five books.
Book One consists of liturgical material. Book Two consists of the accounts twenty-two miracles performed by Saint James. Book Three consists of the story of Saint James’ 
translation from Palestine and burial at Compostela.
Book Four is called the History of Charlemagne and Roland and is a Latin version of the Chanson de Geste known as the Song of Roland with a strong emphasis on the pilgrimage to Compostela.
Book Five is today often referred to as the Pilgrim’s Guide. It is a curious manuscript whose intention has been much disputed. It is ostensibly a guide to travellers to the shrine of Saint James via four roads which cross France and meet beyond the Pyrenees in Navarre where they join to form a single road to Compostela.
There is advice on matters concerning pilgrims such as the inhabitants of the countries they must pass through, which rivers are poisonous, but above all which saintly relics to visit along the way.
Modern historians have attempted to recreate the old pilgrim roads using these locations as markers and filling in the rest with reference to surviving buildings, most often the many eleventh and twelfth century churches which still exist. How well they have succeeded is open to opinion, as is the more difficult question of how much the Pilgrim’s Guide can be said to reflect a true picture of twelfth century pilgrimage.