I have bought all the weapons, last main weapon was altiars sword. There is nothing left to buy in the blacksmiths, is there a secret weapon out there?

I might be wrong, but i think you have to collect some amount (if not all) of the feathers
 
im not that far yet though so i really dont know

You gotta get 50/100 feathers for one of them.

" You gotta get 50/100 feathers for one of them. "

idd, if you get 50 feathers it unlocks a weapon at the weapon and armor vendor, if you buy it the collection is complete.

Thanks, knew I should of put more effort in collecting those feathers!

Ugh, really? I'm only at 25...

ye 50 feathers and you get a warhammer thing, all of them and you get a cape

I've got 89/100 feathers.....man I fucking hate collecting stuff but I want the last cape and the achievements 
 
I'll probably do it later

 just go to this site it has all the feathers mapped out and pictures of each feather 
 
http://guides.ign.com/guides/14302493/page_59.html    

" @Venatio: LOLOLOLOLOL HAVE FUN!   Yeah 50/100 for a war hammer, good unless you have Altiars Sword 100/100 for the Auditore Cape, makes you notorious in every city "

Problem solved.