What is "perduellio"

In the early days of Ancient Rome, perduellio was the term for the capital offense of high treason. It was set down plainly in the Law of the Twelve Tables as thus:

"The Law of the Twelve Tables orders that he who has stirred up an enemy or who has handed over a citizen to the enemy is to be punished capitally.” (Marcianus, D. 48, 4, 3) 1.

Under the terms of this law, those convicted of perduellio were subject to death either by being hanged from the arbor infelix (a tree deemed to be unfortunate) or by being thrown from the Tarpeian Rock. Their families were not allowed to mourn them and their houses were razed.