When a Roman division was punished by decimation only 10% survived. Enough to spread the word about just how bad an idea it is to break Rome's rules. The survivors were the "lucky" ones who had to beat their comrads to death at the point of a sword.
I beg to differ. According to every history I have ever read on the practice, 10 percent of the unit was killed.
From the American Heritage Dictionary:
Decimate originally referred to the killing of every tenth person, a punishment used in the Roman army for mutinous legions.
From the American Heritage Book of English Usage:
If a cohort or legion mutinied, it was decimated, that is, the soldier standing in the first rank in the first file picked a number from one through ten out of a helmet, and the count off continued from that number. When the count off came to “ten” (decem in Latin), that soldier was executed, as was every tenth man after him; the other nine tenths got the message.
It would make no sense for a leader to kill 90 percent of his followers, no matter what their "sin."