The Goblin Wars began in 896 AC and ended in 901. There’s more information in the Highland Gazetteer.
525 | Aaron Paul founds the Order of the Astronomers in Crosspoint Bay |
557 | Aaron Paul and the first monks of the Order of the Astronomers arrive from Crosspoint |
578 (May 15) | The Astronomers christen Castle Kristagna |
587 | Aaron Paul dies |
593 | Taurus, warrior of the Astronomers, turns to shadow with Alazar and Measure |
739-769 | Isaacs’s mnemonic magic adopted by Astronomers |
795 | Clock tower contracted with the Dwarves |
837-839 | Isaiah studies and teaches at Kristagna |
861 | Abiram Forney becomes Master Astronomer |
863-867 | Dungeon excavated by Dwarves |
869 | Jethroh Parthane becomes Abbot |
871 | The Miracle of the Aquarian Pool |
873 | Clock tower built by Dwarves |
882 | Aaron Courlander arrives from Lisport |
884 | The Pact of Four: Aaron Courlander, Philip Carlisle, Zachary Maunder, Frances Nelson. |
887 (June 15) | Peace with the Knights of Illustration |
891 | William Joel Cambel becomes Captain of the Guard |
894 | Aaron Courlander becomes Lieutenant |
896 (May 6) | Castle Kristagna and Stelopolis overrun by goblins |
The descriptions and notes all assume that the adventurers are exploring the ruins in the autumn of 991 AC, 95 years after the castle was overrun.