Dual-wielding
In Assassin's Creed: Brotherhood, Ezio Auditore is able to dual-wield weapons during combat. The pistol acts as a dual weapon to any primary weapon that is a medium-type, like Swords and maces, and the throwing knives act as dual weapons for the short blade (similarly to the original Assassin's Creed). If you have a normal weapon, hold the attack button to aim and release to fire. The poison darts are used with the poison blade.
Dual-wielding weapons offer many more types of counter kills and finishing moves, as well as allowing the player to smoothly shift between long-range and short-range attacks.
Dual wielding is also done by a few enemy NPC's like the Papal Guards and Cesare Borgia, who are both able to dual wield a pistol and a long sword.
Dual-wielding is handy if your enemy blocks alot, or the enemy is The seeker