Sagittarius 4. A great teacher lecturing in an empty classroom.
He spoke, morning and evening, for several hours each day, telling what he knew, imagining questions coming from non-existent students, and then answering them, the questions often leading off into other topics and other realms of knowledge. He know not the bounds or limits of his knowing, for as he spoke he learned more, the knowledge rising to the surface like water from a bottomless spring.
Centuries later the room where that happened became a place where students came to sit, bookless, their eyes closed, absorbing the reverberations which still could be felt faintly echoing from the walls, and which awakened in them other, hidden springs.