The Order of the Mouseion must be considered one of the earliest lodges of magick, although its continued existence has been a well kept secret since the destruction of the Great Library in 47 BC. The sigil of the order is the open book, and it has chapter houses in Alexandria, London and Washington (in libraries naturally.) The mystic lore contained within the Papyrus of Demetrius is guarded even more closely than the existence of the order.
The Order was created by Demetrius of Athens with the foundation of the Great Library at Alexandria, and all the sorcerers who worked at the Library until its destruction were members. There is no written record to verify the fact, but when Caesar wished to make an example of Alexandria to punish its people for the assassination of Pompey, he belived that the order based at the Mouseion would use their sorcery thwart his attack so he persuaded a dragon to join him in the assault with promises of the collection in the Library. All evidence of the battle between the dragon and the Mouseion was destroyed when the Library was burned to the ground in the aftermath of the attack.
What neither Caesar nor the dragon knew about was the hidden entrance to the subterranean complex where the most precious lorebooks were kept, and the order literally went underground. Although most orders maintain their secrecy, the continued existence of the Order of the Mouseion is known only to its members. The Mouseion draws its membership from existing orders, chosing individuals who will adhere to its goals and vetting them carefully before taking a vote on whether they should be approached. A single "nay" vote is sufficient to block membership: only if all the existing masters are in agreement is the prospective candidate approached, and must take a vow of total secrecy before anything is revealed to them about the order.
Candidates for the order are typically scholars, often concerned more with theoretical sorcery than its practise or what they can gain from it. Members are more interested in knowledge for knowledge sake, although they still study new practical uses for existing lore as well as investigating any reports of new lore.