Good chapter, it sets the scene nicely and very descriptively. Mathieu is proving to be an interesting character, his nightmare and reaction at the end reads a lot like post-traumatic stress disorder – there's a lot of potential for conflict there.
Unfortunately I think the descriptions in this chapter are also its biggest weakness.
You're starting the chapter with Servenza, a whole page of description of a city we're only just entering, without a character in sight to put things into perspective. You've done a good job describing the city, but I think it's too early and too much. A lot of what you say is background information that's not particularly important to know right off the bat and with what you do later it's in a lot of places redundant.
For instance, the city has a lot of canals and has some islands. Later on Mathieu is walking through several sections where this also becomes clear, so mentioning those details at the start isn't necessary. I'd start the chapter with Mathieu.
You can also be more subtle with the way you give the reader glimpses of the city instead of telling us all out right in a long summation. In the scene with the tailor you can let the tailor describe the clothing by comparing the pieces to the city, such as 'the slashing in the sleeves, thin and delicate like Servenza's walls'.
Another less than subtle point is how you describe Mathieu – it's not as bad as having the character stare into a mirror, but having him muse about the reasons people aren't staring at him is unnatural. People think in terms of what is and not what isn't. Instead of Mathieu doing the self-description you could've also let the tailor do it. Or skip it, since knowing what he looks like is not really necessary. I got enough from the previous chapter.
