Help on the first decapitation in cinema
 

I remember watching a homage to cinema, or something specific in cinema that i really don't remember but i do remember that the narrator talked about the first ever showing of someone losing their limb/head in movie history. The scene was an ancient graeco/roman movie made in the 00's or 10's showing a massive battle and a guy getting his head chopped off. What movie was this?

Intolerance (1916) has one. That's about as far back as I can go.

Not sure if this really counts as decapitation, but Georges Méliès' 1898 film Un homme de têtes (AKA: The Four Troublesome Heads) utilizes trick photography to show a guy removing his own head.

IMDB Plot Summary:
One of the greatest of black art pictures. The conjurer appears before the audience, with his head in its proper place. He then removes his head, and throwing it in the air, it appears on the table opposite another head, and both detached heads sing in unison. The conjurer then removes it a third time. You then see all three of his heads, which are exact duplicates, upon the table at one time, while the conjurer again stands before the audience with his head perfectly intact, singing in unison with the three heads upon the table. He closes the picture by bowing himself from the stage.

IMDB Link

It's even available on DVD:

Amazon Link

Nope it's not that one i googled

There is at least one decapitation in Ben-Hur (1925) during the naval battle, among many other atrocities, but you probably mean Cabiria (1914).

I believe the first decapitation was in

The Execution of Mary Stuart (1895)

http://imdb.com/title/tt0132134/

They used a dummy :)