Not to be confused with the small crypt inside Basilique St-Seurin, this archaeological site was uncovered in 1910 when archaeologists excavated part of the vast Christian necropolis beneath place des Martyrs et de la Résistance. Open to visitors today, you can descend into its dimly lit depths to admire tombstones dating from the 4th to 18th century, medieval frescoes, amphorae and other ancient relics.
Legend says Charlemagne buried many of his loyal knights here, lost in battle at Roncevaux Pass in 778 after Basque troops ambushed Charlemagne's army on the Pyrenean mountain pass.