This slender tower of purple-black stone is the tallest point in Hive Sibellus and the headquarters for Scintilla’s astropaths. Scintilla’s Astropathic Choir consists of about half a dozen astropaths, the largest concentration of these powerful psykers in the Calixis Sector, led by Senior Astropath Xiao. These astropaths are the only means for contacting other sectors and without them the Calixis Sector would be cut off from the rest of the Imperium. Anyone who wishes to use them to send a message must personally climb the apparently endless spiral staircase up the tower and make their request personally to Senior Astropath Xiao. Each astropath has a different method of visualizing and sending messages, and they spend their lives amid the draughty belfries of the Bastion performing intensive mental exercises and studying the tomes of symbolic code. Aside from a few servitors to assist them, no one lives in the Bastion other than the astropaths.