As the legend goes, in times of the mythical king Mauregato, the Saracen conquerors forced the Christians to pay them a tribute of one hundred damsels each year.

Habían en todo esto de Almanzor dar

cien doncellas hermosas que fuesen por casar,

habíanlas por Castiella cada una buscar,

habíanlo de cumplir, pero con gran pesar.

As the Poem by Fernán González  recounts with amusing anachronism.

This tribute was paid until the reign of Ramiro I, who refused to do so. This led to a bitter war and a decisive battle took place in the fields of Clavijo, near Logroño. The Christian troops were at a clear disadvantage when, suddenly, the apostle St James appeared on a white charger brandishing a blinding sword which he used against the Moors, giving a clear victory to the Christians. This took place on 23rd Mayo 844.

From the book "Curiosidades del Camino de Santiago". by Juan Ramón Corpas Mauleon. Published by Ediles