The gate | ©MarcJP46 / CC-BY-SA
This is the old Saint-Julien gate, named after priory of Saint-Julien, destroyed at the end of the 16th century.
It became Aquitaine gate (porte d'Aquitaine) in 1754, and transformed into an arc de triomphe in 1814, to commemorate the return of the Bourbon royal family on the throne!