Langdon’s lecture at American University of Paris is on the pagan symbolism in the stones of Chartres Cathedral. The building we can see today is a Gothic building built in the the 13th century immediately after the fire of 1194 devastated the 11th century Romance cathedral.
Chartres from its early days as a Christian centre was the destination of pilgrimages. It would have been the centre for ‘pagan’ pilgrimages before Christian faith was established there.
Jean Markdale in his book, “Cathedral of the Black Madonna” says that the cathedral was built on what once had been a druidic sacred site. He says that the ‘Black Madonna’ statues there are examples of the Christian adoption of what had once been a goddess religion.
Chartres Cathedral is full of distinctly Jewish and Christian symbolism expressed in statues of Biblical characters and Christian teaching. However the local folk culture and age-old symbols can also be found. The stone masons who built the cathedral included a wing of stone work dedicated to the seven liberal arts, showing interest in numerology and sacred geometry.
The Chartres labyrinth is another example of an ancient spiritual custom adopted by Christian leaders to provide a contextually relevant form of Christian practice.
The Catholic diocese of Chartres has an official site for Chartres Cathedral – in French.
Wikipedia has a write-up of Chartres Cathedral.