Catienus was angry with Cicero’s brother, Quintus, because Quintus had treated his father harshly and written incredibly aggressive, threatening letters directly to him. [1, 2]

According to Cicero's text in Ad Quintum Fratrem I.2.6, Quintus had sent a letter to Catienus stating that he was "building his own gallows" and that Quintus would see to it that he was "smoked to death to the applause of the whole province." Catienus was physically carrying these letters around Rome to expose Quintus's behavior and ruin his reputation. [1]

The Term Used by Cicero

To describe Catienus's resulting state of anger and hostility, Cicero uses the Latin word "iratus"(angry/incensed).

Slightly earlier in the text, when discussing the broader political fallout of Quintus's sharp tongue and why people are so deeply offended by his behavior, Cicero famously uses the phrase "iracundiae vigor" (the violence/intensity of your passion/wrath) to describe the hostile environment Quintus's temper was creating among the provincial Roman knights.

If you are analyzing the linguistic style of this letter, let me know if you would like to explore how Cicero contrasts "iracundia" (a habitual tendency toward anger) with a temporary state of being "iratus" (actively angry).