Ares' Sword

Ares' Sword is the sword used by Ares, and might be his symbol of power.

Appearance
Ares' sword is a very large two bladed sword. The hilt is a skull with a ruby in its mouth. To mortals it looks like a shotgun due to the mist. When in its cover form (like Riptide being a pen), it's a baseball bat. It can be turned into any other weapon imaginable. When Percy was fighting Ares in The Lightning Thief, it seemed to grow longer and longer as he got more and more furious

The Lightning Thief
In The Lightning Thief, Ares uses it in a fight against Percy in a duel at a beach in Los Angeles, after Percy taunts him. Mortals that saw the fight mostly thought it was a shotgun due to the mist.