Four Cards

The Four Cards are found on ancient shrines on Ambrosia in Ultima III. They are the only way for the party to destroy the machine part of Exodus in the Castle of Fire. This implies that they are either some kind of programming cards, or some kind of destructive hardware.

Stranded on the lost island of Ambrosia, the Stranger searched through four ancient shrines and found the four ancient cards of Love, Sol, Moons and Death. As he/she already knew, these cards could be Exodus' doom. But only after talking with the Time Lord in the Dungeon of Time, he/she knew what to do exactly. Fighting their way through the Castle of Fire, they arrived at the machine core of Exodus. Inserting the cards in the right sequence, the machine exploded. This was the end of Exodus.

With Exodus' destruction, the Four Cards ceased to exist.

Trivia

 * That the cards appear in the museum in Ultima IX is a big error, since they vanished into the machine, which exploded shortly after.