Because of its nature as a palatine basilica with a cloister on the north side and the Royal Pantheon to the west,
the church of San Isidoro features two substantial southern entrances. The passage to the nave was through the Puerta del Corderón or Door of the Lamb, so called because of the Agnus Dei which surmounts the sculpture of the porch tympanum.
Two spandrel figures loom down from either side of the tympanum – Saint Vincent and Saint Isidore whose relics were guarded by the monks of the royal abbey.
Depicted on the sculpture above the doorway is the Old Testament narrative of the Offering of Isaac. From the Visigothic church of San Pedro de la Nave near Zamora to the capital relief at Jaca, this subject seemed to hold a special fascination for the Christians of medieval Spain.
At León the full import of its meaning is manifest. The separate fates of Abraham’s two sons, Ishmael and Isaac were central to medieval Apocalyptic prophecies concerning the conflict between Christianity and Islam.
The Offering of Isaac, according to numerous exegetical writings was considered a prefiguration of the Crucifixion, a connection made clear at León with the presentation of Isaac riding towards his fate at Moriah on an ass, as Jesus made his Entry to Jerusalem before the Crucifixion.
In the Genesis text it is written of Abraham’s seed of the line of Isaac that a great nation would be born and that they would come to possess the gates of their enemies.
Ishmael, Abraham’s son from his bondswoman Hagar had been exiled to the desert, however and the race of Ishmael had long been identified with that of the Arab invaders of Spain.
It was helpful that Saint Isidore himself, had made this equation in his Etymologiae. “The Saracens live in the desert”, he wrote. “They are also called the Ishmaelites, as the book of Genesis teaches, because they are descended from Ishmael. They are also called Hagarenes because they are descended from Hagar. They also, as we have already said, perversely call themselves Saracens because they mendaciously boast descent from Sarah”.
On the tympanum of the Puerta del Corderón, opposite Isaac and Sarah are Ishmael and Hagar. Hagar with her skirt raised in the licentious pose associated by the Christians with the Saracen race and Ishmael, an archer as recorded in Genesis, wearing the attributes of a contemporary Saracen cavalry warrior, a turban and the short stirruped saddle.
The identification of the northern Christians in their war of Reconquest against the Moors of Spain with the triumphant destiny of Isaac’s line had an established tradition deriving from a previous exegetical text known as the Chronica Prophetica which promised the liberation of the Visigoths from the yoke of the Ishmaelites. The Chronica, written in 883 drew upon Ezekiel’s Apocalyptic warnings concerning the people of Gog. ”Certainly Gog is to be understood as the people of the Goths and just as Ishmael is written above to signify all of the race of the Ishmaelites when the prophet says, “Set your face against Ishmael.”
Above the patriarch Abraham, a pair of angels hold aloft an image of the Lamb in a pose of apotheosis.
The Lamb is both that of the Eucharist, signifying the New Covenant and Apocalyptic in fulfillment of the prophetic context of the Genesis story and the medieval conception of the war between Christianity and Islam as part of the eschatological working of history towards the End of Time.
Although historians have not been able to give a definitive dating for the Puerta del Corderón, the decade of the 1140′s is often favoured. This coincided with the reign of Alfonso VII and the escalation of the Reconquista into a contest for the whole of the Spanish peninsula and the visit of the abbot of Cluny, Peter the Venerable who had begun the institution of an ideological war against Islam.