Upon Michel's journey across Bath, England, he had discovered a Piece of Eden called the Aegis, a technologically sophisticated battle suit which was worn by the First Civilization member Minerva in battle. Michel was presumably driven crazy by the Aegis and chose to hide it away in this very vault.
He had created discs imbued with the Assassin insignia, and had hidden them in Music boxes which were scattered throughout London.
In 1868, Jacob and Evie Frye discovered the vault as well as all the music boxes which contained the discs and used them to open up the vault to retrieve the Piece of Eden stored inside. It is unknown what happened to the vault afterwards.