Excalibur is the legendary sword unlocked in Assassin's Creed Valhalla by finding 11 tablets.
Eivor can obtain the weapon in Myrddin's Cave in Hamtunscire. Eight of the tablets are hidden in special caves and other locations around England, while three are carried by powerful Zealot enemies. After collecting all 11, Eivor can place them in the stone pillars inside the cave and draw the sword from its resting place.
The weapon is an Isu-era relic within the game's mythology, although its presentation deliberately connects it with the medieval legend of King Arthur's sword. In gameplay, Excalibur is a greatsword with a distinctive radiant appearance and powerful area effects when used in combat.
This quest is separate from Valhalla's other mythic weapons and bows. The 11-tablet requirement is the key identifying detail: several special weapons can be found in the game, but Excalibur is the one tied to this specific collection challenge.