The hills

The alluvial plain was bordered and dominated by a series of hills created during the Tertiary Era:

• On the left bank, there were the hills at Tolbiac, Montparnasse, the plateau at Villejuif. the Butte-aux-Cailles was located next to a meander of the river Bièvre, and the Sainte-Geneviève hill was a promontory overlooking the Seine.
• On the other side of the river, a series of raised zones were arranged in an arc (the hills at Chaillot, Ménilmontant, and Buttes-Chaumont, the hillocks of Etoile, Auteuil, Montmartre and Belleville) interspersed with valleys like that of La Chapelle. This series of hills separated the Parisian basin from La Plaine de France. They were located north of the original path of the Seine, which probably captured some of their runoff water.