I think this is what it is all about. An ultimate twist, a cruel fate.
The Forerunners created the Flood and used it against the Precursors, wiping them out.
The Flood then evolved and turned on them.
Short, sweet, and to the point.
This is the act of barbarity described in Silentium.
Discuss.
[Edited on 08.29.2012 11:34 PM PDT]
-
We already know that the Precursors created the Flood though, and the ships which Ancient Humanity discovered them in wasn't of Forerunner design.