Archeus is easily one of the best weapons early on (along with Cruel Barb), and while its usual damage per second isn't stellar (but still good), its proc effect nearly doubles that, when the chance hit connects. This is also the only sword in the game that you can put a level 35 enchant on, and use in the 20-29 pvp bracket.
Acherus is often misspelled Archeus by newer players.
Archeus is the sword of Morgan Ladimore, a soldier from Darkshire who fought for the Alliance in Lordaeron. After the death of Uther the Lightbringer, he returned to Darkshire to find his wife and two of his three children dead, and subsequently went mad, eventually killing a group of cemetery custodians who came to investigate. Committing suicide, Ladimore returned as the beast Mor'Ladim, haunting the cemetery of Raven Hill until he is destroyed by adventurers working on behalf of Darkshire. Delivering his daughter's ring to his grave outside of Raven Hill, Ladimore's spirit personally gives his sword to those who defeated him, hoping that they would use it as he had once done - in defense of all that was good and decent.
This item is a reward from the Alliance quest which starts with Watcher Ladimore in Duskwood. To complete the quest, you need to visit the Weathered Grave outside of Raven Hill Cemetery, north of the Forlorn Rowe. The quest is part of a chain which starts at the grave as well.