The use of lions in medieval religious and political art hews closely to the traditions inherited from around the Mediterranean. Lions were symbols of dominance and protection. With the fall of the Roman Empire, European direct experience of actual lions becomes quite rare. Medieval representations of lions are simulacra of the real thing--copies of copies. The lion as symbol is the pervasive and persistent understanding, and the representations which were most realistic were sourced from manuscripts originating in the eastern part of the surviving Roman Empire, or from discoveries of sculpture dating from the Roman era in Europe.
San Zeno, Verona
The Church adopted the guardian lion theme from pre-Christian palace models. In Italian medieval churches in particular it is common to see resting lions supporting columns which flank the western entrance.
Santa Maria Maggiore, Bergamo
These lions might be presented as protecting figures, as seen in the entrance to the duomo in Bergamo, where the lion in the background protects its young, and the one in the foreground appears to protect a man in a cassock.
Cathedral of San Nicola Pellegrino porch, Trani
The cathedral in Trani was situated right on the water at an embarkation point for armies (largely mercenary forces) to sail east to fight in the Crusades. The lions on its facades are engaged in fighting enemies of the Church, such as this African figure here (note the stylized curly hair), who is meant to represent Islam. This church was a place to get the soldier's mind-set right before his mission.
Cathedral of San Nicola Pellegrino portico, Trani
Directly above the lion wrestling the African figure, one can see another lion sitting atop an elephant. The lion's head turns West (toward Rome). In this case, the message is conquering the East (as in Asian or Middle-Eastern threats). Medieval manuscripts would often symbolize the non-Christian east with elephants and tigers.
Saint Gilles du Gard Abbey, Provence
On the pilgrimage road to Santiago de Compostela, the monastery at Saint Gilles was a very popular stop, where numerous relics were available to pray before. This lion, beneath a bas-relief of Saint James, gnaws on a figure which represents a heretic (or possibly a pagan). The figure is near-naked, with a hairstyle and beard which evoke Gaulish styles under the Roman conquest. This lion appears to have originally had bright glass studding his muzzle, and jewel-like eyes. He affirms that pilgrims will be protected from spiritual threats.
Basilica of Sant'Ambrogio, Milan
This lintel at Sant'Ambrogio captures one of the most frequent tropes of Church-as-Lion confronting a symbolic enemy: Lion versus Dragon. The dragon is a catch-all for many evils--paganism, heresy, worldliness, Abrahamic others.
Fermo Church, Le Marche
This lion seems a bit intimidated by the dragon, but the expression may be more of a factor of the artist's guesswork around lions. The dragon seems to be rendered with more enthusiasm and detail). The placement of lion and dragon confrontations at transitional spaces (door-frames, namely) suggests that one message is that the lion protects the faithful inside from the dangers outside. Monsters such as gargoyles and dragons on the exteriors of churches emphasized the spiritual dangers from which the Church offered to defend the believer.
Misericord, Saint Pierre Cathedral, Poitiers
The theme exists not only in stone sculpture, but also in wood-carving, as the backing of this fourteenth-century misericord attests.
Fermo Church, Le Marche
Some romanesque lions seem to be created for the sheer joy of it. It's not clear on this weathered sculpture what/whom the lion was devouring, but the flowing mane and open, panting expression make him seem positively dog-like.
French Romanesque Capital, Philadelphia Museum of Art
And this capital, with its lion a spiral of curling locks and curving tail, seems like an artistic triumph more than an assurance of protection.
Altar Capital, Sainte Radegonde Church, Poitiers
In the Romanesque period, undulating patterns (somewhat streamlined from Celtic design) become more popular, and creatures, even based on real animals, become more fanciful. At Sainte Radegonde, these lions are, in medieval art history parlance, bi-corporal, or monocephalic. They may be here to assert protection at the altar, or to invoke the idea of Christ as lion, but the overall effect is exuberant, delighting in the optical illusion of a single lion on the facings, with the bodies conjoined in a series of curves at the corners.
San Marco and Lion, 5th century, San Vitale, Ravenna
Perhaps the most common use of lions in church art, both interior and exterior is to represent the Gospel of Saint Mark as one of the tetramorph. In the mosaic above, the lion appears as a protector of the evangelist, who has his gospel ("Secundum Marcum" is "According to Mark") on his lap, along with his stylus and ink at his right side.
Lamb of the Apocalypse with Tetramorph, 12th century, Pomposa Abbey
The lion as part of the tetramorph is used in relgious art programs which depict the Apocalypse. The four figures, mentioned in the book of Ezekiel and in Revelations, appear in John's vision surrounding the enthroned king. The lion (lower-left) seems to be placeable in any order in tetramorph representations, regardless of the ordering of the four gospels in the New Testament.
Bronze Lion, circa 15th c., Orvieto Duomo
This bronze statue shows that the artist took pains to create realistic musculature, wings, and a strong feline face, but, as with many of these depiction, the mane is where he took liberties to create aesthetically-pleasing rhythm and symmetry.
For Part 3 of this topic, I will focus on some less-familiar uses and themes of lions in religious art, including lions from medieval Islamic and Jewish art. If you are interested in pre-Christian uses of Lions please read Part 1 of this topic.