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.
"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
But over time with the expansion of the rights of Roman citizens, the use of corporal punishment lessened until the time of Augustus when conviction only carried with it the punishment of aquae et ignis interdictio (exile).2
The trial was conducted by the duumviri perduellionis, who during the Monarchy were appointed by the king. Later on during the Republic they were proposed by the consuls and formally appointed by the comitia ( comitia curiata or comitia centuriata). The judgement of the duumviri was subject to appeal, which generally was tried by the comitia centuriata unlike in Horatius' trial.3 The prosecution was led by tribunes or aediles.
By the late Republic, the archaic perduellio had become largely obsolete, though it could still be used (see Gaius Rabirius). Its offenses were covered by the law of maiestas which included a broader range of crimes. Perduellio became the designation for a particularly odious type of maiestas.
1The Early History of Rome: Books I – V of the Ab Urbe Condita. Translated by B.O. Foster. 2005 ed. Published by Barnes & Noble, Inc. New York, New York. 34-36
2A Summary of the Roman Civil Law. Patrick Mac Chombaich De Colquhoun. 3rd Ed. V. and R. Stevens and Sons. 1854. 638-639.
3“Perduellionis Duumviri”. A Dictionary of Greek and Roman Antiquities. Ed. William Smith, 1870. Pub. John Murray, London, 1891. 886.
- Smith's Dictionary of Greek and Roman Antiquities
- The Law of the Twelve Tables: (Latin); (English)
- Ab Urbe Condita, Books I-X