The Diadem is a massive, abandoned megacity on Palisade.
It was dug into and along the entirety of Palisade's equator thousands of years prior to the beginning of PALISADE, perhaps as an "extremely arrogant" architectural project.[1] Along with countless shops, arcades and other unused or partially built structures, it contains the wreckage of an ancient mech battle. Deep below, it houses the Fundament nodes, which the Cause and the Authority both wish to control.
The Temple of the Threshold is located on a bridge over the Diadem.