Erinon's Axe is a weapon of ancient times, thought lost in the War of Imbalance long, long ago. The Axe is known not only for being a strong weapon, but also for the power to significantly raise the user's combat ability; even the most clumsy warrior can use it to great effect. The weapon was once thought lost, but time travel through the Amulet of Balance revealed the truth. The Avatar took it into the present time, thus returning this weapon to the world.
In Ultima VII Part Two during the Silver Seed quest, Erinon's Axe can be found in Aram-Dol's lair in a chest, once the liche has been dealt with. Giving this weapon to the weakest party member can truly pay off; Gwenno or Petra, who don't have much experience when they join the party, both make excellent choices.