“You don't deserve to learn what this place has to teach us. Never have, never will!”
Antiquis Triangulum served as the resting place of the ancient creatures, of which His Eminence is a member, during the Ice Age. To save their species from dooming fate, the creatures chose two of their strongest members, including His Eminence, to be sealed away in sarcophagus. The Pyramid was to be opened up one day during the solar eclipse. Accroding to His Eminence it all was done to "bring [his] people back to the surface. To take back [their] world from... walking, talking primates."
At the dawn of 20th century Elizabeth Mann, Art Wurst, Maxwell Finnwich and Lo Ping, attenders of A Nigma High, joined with their principal, Alexander Nigma, to open the Antiquis Triangulum during the eclipse. The four children transported the eclipse beam to the Pyramid by reflecting the light to each other. When it opened, Alexander Nigma stepped into the Pyramid and used the cipher to see what was in it. Inside he came across the surviving reptilian creature, His Eminence. The two involved in a fight, when Alexander Nigma got trapped in a closing Pyramid while His Eminence escaped. The Pyramid became a deathbed of Alexander; his skeleton could still be found there.
After that eventful day, other people had tried to open the Pyramid again to learn all its secrets and wisdom, but mostly failed to do so. Notably, Niles Peg tried to open the Pyramid with the knowledge contained in the Book, but did it incorrectly, causing him to fall into coma. Lynch Webber ("Pyramid Scheme") and Kerrigan ("The Hydra") did the same thing years after him and were doomed to fall into coma as well.
In show the Pyramid first appeared in "Outcast Times at A. Nigma High", where the characters used it as a staircase to exit the tunnels. While it did not have much significance at the time, the Pyramid later became the centre of chaotic events of Season 3.
In season 4 the Pyramid was opened up successfully by Finnwich and Lee Ping ("Follow That Finnwich"). Before the Council could use the Pyramid's wisdom in its deeds, Finnwich blew it up. Fateous made the mistake of going in, seemingly being killed off by explosion. The Pyramid was tasked to be restored by Art Wurst clones, using A Nigma High teachers and students, among which Camillio Martinez and Brandy Silver recognized the wicked plan and sabotaged the process.
In season 4 finale Fateous Mann was last seen alive, leading the army of lizarmen sealed away underneath the Pyramid.
It was revealed that the Pyramid contains an unearthly power and all the mysteries of the world. Technically it can only be opened during a solar eclipse by using two keys, one of which had been in Lee Ping's possession since Season 1 ("15th Graders"). It is shown that it is protected by the cybernetically-enhanced Blue Tatzelwurms. The Book seems to contain information of the Pyramid, but it is in a language that only Finnwich has been shown to read.
- The Pyramid's name, Antiquis Triangulum, is Latin for "ancient triangle".
- The place where the two keyholes are located resembles the triforce from the Legend of Zelda series.
- Inside the pyramid there are ciphers in the same language as the one used in the Book. The Book seemingly contained the information of Pyramid's successful opening before that particular page had been ripped out by Finnwich.