It was built by Operation Ark's senior administrators (known to the Safeholdians as "archangels") under Eric Langhorne, and served as the seat of the Grand Vicar as the Archangel Langhorne's steward on Safehold. The Plaza of Martyrs stretched out in front of it.
Merlin Athrawes deduced that it had been constructed after Langhorne and most of his inner circle were killed by Pei Kau-yung, and that its builders had used armorplast and other highly advanced construction materials, remarking that the building would likely outlast the mountains surrounding Zion.
Merlin also discovered the presence of active energy signatures beneath the Temple. Though he cautiously attributed these signatures to the structure's "miraculous" climate control systems, he also decided that using the high tech surveilance systems available to him would constitute an unacceptable risk of detection. This prevented him from directly observing the meetings of the Council of Vicars, in particular the Group of Four. (OAR)
Merlin eventually discovered the true source of the Temple's energy signatures. (HFAF)