Final Fantasy XII - PS2/Cheats

From WikiCheats

Obtaining the Zodiac Spear
It's slightly underhanded the way Square-Enix hid the most powerful weapon in Final Fantasy XII. The Zodiac Spear is inside a chest in the Cloister of the Highborn within the Necrohol of Nabudis, but it will only appear there IF you have not opened the following treasures throughout the game:

1. The chest in front of Dalan's home in Lowtown.
2. The chests in the southeast corner of the Cellars in the Palace of Rabanastre.
3. The middle chest containing 316 Gil, in the Confiscatory of Nalbina Dungeon (where you reacquire your confiscated weapons and armor).
4. Any of the sixteen chests located on the southeastern island of the Vaddu Strand of the Phon Coast.