On the events prior to the War of Assassins of 10, 187 AG, the Archducal Palace had already been restored from the damages some years ago. It was there where Archduke Armand Ecaz received his future son-in-law Duke Leto Atreides and some members of the Atreides household.
After the assassination attempt during the wedding of Leto Atreides and Ilesa Ecaz on Castle Caladan, Prad Vidal, Duke of Elacca (a continent of Ecaz) and vassal of Archduke Armand, informed all the Ecazis that their ruler had been murdered along with his heiress Ilesa, and several members of House Atreides while the wedding took place. However, as soon as the Archduke arrived in Ecaz escorted by the Atreides army, Prad Vidal and his supporters fled from the Archducal Palace' Hangar to his estates on Elacca, where he planned to resist and provoke a Civil War.
After Vidal's assassination by Duke Leto and Gurney Halleck, Archduke Armand assembled his forces and moved to Grumman, where he was going to revenge from House Moritani, supported by the Atreides army.
After Emperor Paul Atreides' speech at the Imperial Hall of Oratory on Kaitain, Archduke Armand, heirless and tired of politics, submitted his realm to the Fremen Jihad's forces, and retired to his estates on Ecaz, in especial, to his ancestral home, the Archducal Palace.