The Riyria Chronicles7 books in series
The Crown Tower Summary
Hadrian, a warrior with nothing to fight for, is paired with Royce, a thieving assassin with nothing to lose. Together they must steal a treasure that no one can reach. The Crown Tower is the grandest fortress ever built and home to the realm's most prized possessions. But it isn't gold or jewels that their employer is after; if he can keep them from killing each other, they might just get him his prize.