Atop each beacon hangs, as if suspended in mid-air, one of fourteen Gongs, each zealously guarded by a Gong-Keeper, and struck only in times of trouble or need.
The Gongs make no audible sound yet their mystic vibrations resonate silently along the Skray Lines, unnoticed by all but the Gong Wizards high in the Listening Tower of Astriel.  Day and night the Tower is manned by  a rotating watch of four wizards who listen through two giant amplifying horns. In the upper chamber of the Listening Tower, the sources of Gong strikes are plotted and missions planned.  Then from the terraces of Astriel, the Gong Wizards fly out on their sorties across the length and breadth of Wildergorn.
From The Book of Wildergorn