Peer gems appeared first during time of Exodus (before, there were other ways to look at the map; see Trivia below). They could only be bought at the illegal guild shops and were quite expensive. This didn't change in the Age of Enlightenment, although monsters could often be found carrying them. By the Gargoyle invasion, any tool shop sold them. After the time of the False Prophet, they vanished without a trace.
- The gem given by Lord British at the beginning of Forge of Virtue in a way also works like a peer gem, only it showed one special place.
- The spell "Peer" fulfilled the same function as these gems, as did any crystal ball encountered in Ultima V.