The shell, as an emblem of pilgrimage, "signum peregrinorum", has been in use since at least the twelfth century, but despite other pagan and Christian uses throughout the centuries, it began to develop enormously in the medieval period as a heraldic element, a symbol of Santiago : of its cathedral, its city, its pilgrims ... The scallop shell became synonymous with Santiago and was used on the facades of palaces, as well as on coats of arms and on tombstones.
Since ancient times shells were invested with multiple meanings, assuming different pagan functions - symbol of love or talismans to protection against ‘the evil eye’, magic spells or diseases in general – or the Christian era, as a baptismal symbol or one linked to funeral rites as a symbol of resurrection .
The first examples of the use of the shell in the world of pilgrimages go back to the beginning of the twelfth century. Among the artistic representations the critical literature has agreed in emphasizing the relief of the western portal of Autun, whose tympanum dedicated to the Final Judgment and where the shell appears on the spores of two pilgrims as symbol of resurrection. From then on, and coinciding with the Golden Age of the "major pilgrimages," the role of the shell as a Jacobean emblem was consolidated.
The shell Pecten maximus as a souvenir or signum peregrinorum, sold by the merchants in the shops of Compostela and sewn by the pilgrims in their clothes and hats, was one of the eminent "products" of medieval European marketing, probably invented or, at least, promoted during the bishopric of the wise( or wily) Diego Gelmírez.
In the middle of century XII the Codex Calixtino refers on three occasions to the shell "vieira" bestowing on it two different meanings. On the one hand the Calixtino still refers to ancient pagan uses of the shell, attributing to it the 12th miracle of the second book or Liber miracolorum, when a crusader is cured through contact with it, as if it were an amulet capable of curing or preventing diseases.
The other two references in the Codex refer to the role of the scallop as a Jacobean emblem, in the celebrated sermon Veneranda Dies and, again, in book V, known as the pilgrim's guide, which contains the important shell trade that already existed in the city. This commercial activity would have at first used real molluscs collected on the beaches of the nearby Atlantic coast, while with the passage of time the establishments would have begun selling mainly reproductions in metal and jet which occupied a large part of the enormous market of pious objects existing in 12th century Compostela.
Why was the shell chosen? Probably because it was an object that could be collected free of charge and in large quantities on the nearby coast in the Land of Santiago, an emblematic, natural and organic object as the only insignia known at that time , and the Galician equivalent of the palm that pilgrims and crusaders brought back with them on their return from Jerusalem.