Medieval Paris was full of religious buildings - in the 14th century there were more than 80 churches, abbeys monasteries!
Abbeys owned huge swathes of land on the Left Bank and would teach thousands of students, who would be seen walking around Paris - instantly recognisable by their tunics and special haircuts.
Two of the most famous abbeys were Sainte Geneviève and Saint Germain des Prés ("of the fields").
You can still see their towers in the Lycée Henri IV and the square of Saint Germain des Prés.
Other spectacular ruins from this period include the Abbey Saint Martin des Champs (today's Musée des Arts et Métiers), the Convent of the Cordeliers and the College des Bernardins.
The construction of Notre Dame was also in full swing - and lasted 200 years.
Check out our dedicated walk on the topic : Secrets of Notre Dame.