Regarding your inquiry regarding the so-called "astrariums," it is our considered belief that these are relics from a cult that existed in the pre-Andrastian era of the Tevinter Imperium. Now, what would be considered a cult in a society that worshipped the Old Gods? An order of magisters who believed in the destruction of the Magisterium, the governing body of the Imperium that determines which mages are and are not given the "magister" title. The members of this order wished to return to an earlier period where Dreamers ruled, and evidence indicates they operated throughout Tevinter, though primarily in the frontier areas. There they would lock away their secrets, caches of treasure, and perhaps even secret meeting places (though we have no way of knowing for certain), unlockable only through knowledge of ancient astronomy—a practice that was, we understand, rather out of fashion in the late Tevinter period.
According to our investigations, each of the astrariums could point to the secret cache if one knew the three constellations that mapped to each device present at the site. Connect the dweomers in the correct configuration, and it would be revealed. Many of these relics were sought out by Andrastian cultists in the early Divine Age (the Order of Fiery Promise in particular) and destroyed. Why? Because they believed the astrariums held together the Veil, and that destroying them would destroy the Veil and thus the world. Such is the way of cults of any kind that the true reasons for what they do could never truly be understood by modern minds.
—From a letter written by Magister Pelidanus, head of the Corial Order, 5:12 Exalted