For those who'd like to use french as a basis for your toponymy, there are a few facts that are worth knowing (especially if you plan to give it a medieval feeling).

Lots of places are named (as in any language, I guess) after landmarks : rivers, hills,... or after what the place was used for in the first place.

For example, if you want to use landmarks :

- The french city of Bordeaux is named after the fact it is a coastal city. Bordeaux a contraction of "bord des eaux", which could be translated as "water side".
- The town of Liège is named after a small river that crossed it before it was "forced" underground, the river Légia.
- You can find a whole lot of places with names like Montrouge (red hill), Le Chesne ("chesne" is an old form of the word "chêne", which means "oak tree"),...

Places named after what they were used for :

- There's a neighborhood in the city I grew up in called La Bergerie (the sheepfold). Of course you won't find any sheep, but it's what it used to be.
- There are villages called La Forge (the forge), Vieux-Moulin (old mill),...

A lot of place are named using ancient words. This is what makes french medieval places sound "medieval"... You can use oldish versions of some words quite easily :

- The word "château" (castle) used to be "castel" (as in Castelnaudary, the new castle of Ary, or in Castelsarrasin, the Saracen castle)
- The word "royal" (related to the King) used to be "réal" (as in Montréal, the King's Hill)
- The word "nouveau" (new) used to be "nau" (like before, in Castelnaudary, which we can decompose as "castel nau d'Ary", the new castle of Ary)
- The word "libre" (free) used to be "franc" (as in Villefranche, free city)

People who named the places liked to show how new they were :

- Chateauneuf-du-Pape (Pope's new castle)
- Villeneuve-d'Ascq (the new city of Ascq)
- Neufchateau (new castle)
- Funilly enough, the "Pont Neuf" (new bridge) in Paris is the oldest one in the city

Of course, we also have more than a few names that come from other languages : latin, german, flemish, italian, spanish,...