Even though there hadn't been any danger coming from the river Seine for the past three centuries, possible invasions from the Normands were still feared by the inhabitants of Paris at the beginning of Philip-Augusutus' reign.
The king decided to build an impregnable fortress where the defense of the city was the weakest.
The unused land at the end of the wall touching the river was called the "Louvre". The origin of the name is still unknown despite some unsatisfactory explanations. He built a genuine fortified castle with a dungeon, surrounded by a wall, with a fortress inside. It was only as a quarter the size of the present "Cour Carrée" .
The dungeon was a huge square tower; ist shape can still be seen i on the ground. It was about 32 yards high, up to a cone-shaped roof., 15 yards in diameter and the wall was 4.20 yards thick at the bottom.
Inside the wall there were rooms one could access by way of a spiral staircase. There were no underground prison cells. A 6 yards deep moat surrounded the wall, full of water flowing downhill from Belleville and the Prés St Gervais.
Around the dungeon there was a wall: 77 yards from north to south, 70 yards from east to west, very thick on the western side, only because the Scandinavian danger had come from there. Two crenelated towers on each corner, as well as living quarters finished the construction.
As the western wall was particularly solid, it was kept when the Louvre was rebuilt by François I (who reigned from 1515 to 1547). The main entrance to the fortress was through south, though there was a smaller one on the eastern side.
The king would keep his treasure, his archives and his arsenal in there, but he never lived there. The archives had been lost in 1194 and rebuilt.
Picture taken in the Louvre museum - history section 1st part (march 2011)