We can see a Latin sentence, below the nave’s cornice: we don’t know what it is… The text says:
Obsecro vos, fratres, aquilonis vincite partes Sectantes claustrum, quia sic venietis ad austrum. Trifida quadrifidum memoret succendere nidum ignea bissenis lapidum sit ut addita venis. Pax huic domui.
Which means: ″Brothers, fight against the aquilon and come in the cloister, and you’ll be next to the auster. The 4 parts nest will be invade by a flaming peace, arriving by the 12 veins of the stone.″
Gibberish? No, wait! The book explains that this inscription was used by monks when they had to go to the lavabo for a wash, who was in the middle of the cloister.
To go in the cathedral, they went from the aquilon (a cold wind from the North, representing the Devil) to the auster (a hot Southern wind). The nest was where the monks lived, and the veins the cloister’s galleries! Whoa...
Like the famous French writer Stendhal wrote in his novel Mémoires d'un touriste (part I): maybe it was an advice, to warn monks about the climate’s rigour, about the wind’s strong blow?
To say to them where was the best place in the cathedral or in the cloister to enjoy the sun’s heat in summer and protect themselves from the icy wind in winter?
The famous historian Prosper Mérimée had the same idea, when he wrote the following translation in his book Notes d'un voyage dans le midi de la France: monks had to bear the cold wind from the North, which attacked them in winter.
If they wanted to escape from it, they had to take shelter to the South, in the Cloister. They had to find their own interior flame (by praying) in order to warm their cells up...