Not a sword, but a bayonet! Well, maybe a sword, since at this time, the bayonets were designed so that they could be used as swords, but you can clearly see that this was designed to be locked into place on a firearm (note the little notch in the back of the hilt). The downward curve of the blade is certainly so that the projectile does not damage the tip during use. The curved tip of the hilt (otherwise known as a quillon) allowed the soldier to increase his reach when attempting to stab his opponent. It could also be used to brace the gun for precision stabs.

Anyways, a quick Google search yields this, the French Chassepot Bayonet, Model 1871. The inscription reads something like: Mdle (Modèle) De Chat (Château) MAC (perhaps Manufacture d'Armes de Châtellerault)? 1871. Certainly a forger's mark/seal describing its location and date of manufacture.

The gun that this bayonet was attached to was regarded as one of the best rifles of the Franco-Prussian war (1870 - 1871). It was also famously utilized against Giuseppe Garibaldi's troops at the Battle of Mentana in 1867. This is certainly an impressive find, since sword bayonets are generally rare, even moreso ones that date from before the First World War. It also looks to be in very good shape considering its age. A collector's item for sure.

I'm sorry to be breaking the 20-years rule, but for reference, it looks like there's a similar bayonet on sale here. The last picture, specifically, has some similar inscriptions.