Philippe Auguste's fortification

Saint Germain des Prés is a district of Paris where the first kings, named Merovingiens decided to be burried, actually in the Abbaye. Later, during the XIIItn c., king Philippe Auguste wanted Paris to be protected against ennemies, and he built a big fortification around all over what was the city (and the abbaye remains outside); marks & elements of that fortification still remain in the area: stone towers, walls..

A very nice & documented site (fr) present this extraordinary piece of architecture:
http://www.philippe-auguste.com