To get this achievement early you can buy a legendary armor set from the Ubisoft Club (need to sign-up from the game menu).
Press start and then Left on the D-Pad to get to the Main Menu and select Ubisoft Club. From here you can buy Ezio's Roman Armor set (FREE at the time of writing). The only requirement is that your character is at Level 4.
Next go to the Inventory screen to equip the entire armor set (Ezio's Roman Hood, Vambraces, Robe, Sash, Boots & Milanese Sword).
Doing this also unlocks: