This church was also known as Saint-Sernin-du-Taur, because originally it was dedicated to the first bishop of Toulouse, Saturnin or Sernin.
The legend says he died from his torture at the current location of the church: he was tied up at a bull's tail, dragged on ground to the Capitole... That's why the church was called Taur (from French word taureau, “bull”)!
Anyway, saint Hilaire raised here a little wooden oratory in order to house Saturnin's body, in the beginning of the 4th century. The relics were translated in the 5th century, in the brand new basilica: the current basilica of Saint-Sernin!
And yet, they kept the small oratory! At the end of the 6th century, it was extended by duke Launebolde. But the current church dates back to the 14th century, rebuilt when the district was transformed and inhabitants increased.
Oh, by the way, this church looks like the church of the Dalbade, in Toulouse! Same fortress look, same strong silhouette in a narrow street... Anyway, the famous Cadouin's shroud was here, in 1455! Yes, in a small lateral chapel, with vaults decorated with the abbey's coat of arms... They put this Holy Shroud here in order to save it from the Hundred Years War's destructions.