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.³

As the concept of national sovereignty took hold in Rome, perduellio also came to mean an offense which “injured or brought into danger the dignity, supremacy, and power of the commonwealth [Roman State]”. This included such things as losing an army, violating the rights of the tribunes of the plebs, or usurping a function of the State (as in case of Horatius)².

In the Ab Urbe Condita, Livy recorded the first instance of both a trial of perduellio and appeal:

"It enraged the fiery youth to hear his sister’s lamentations in the hour of his own victory and the nation’s great rejoicing. And so, drawing his sword and at the same time angrily upbraiding her, he ran her through the body…The king…said: “In accordance with the law I appoint duumvirs to pass judgment upon Horatius for treason [perduellio]. The dread formula or the law ran thus: ‘Let the duumvirs pronounce him guilty of treason; if he shall appeal from the duumvirs, let the appeal be tried; if the duumvirs win, let the lictor veil his head, let [the lictor] suspend him with a rope from a barren tree [arbor infelix]; let [the lictor] scourge him either within or without the pomerium.’ Even though the duumvirs found Horatius guilty, Horatius was allowed to appeal (to the people) and by them was acquitted. However, Horatius’ father had to perform expiatory rites and Horatius himself was forced to pass under the yoke." (Livy, 1.26)¹

...
Wikipedia