Not “important” — legally untouchable. Rome’s tribunes were sacrosanct in the literal sense: harming one was a capital, religiously sanctioned offence, not just a political scandal.
The Latin sacrosanctus described a specific, concrete legal status in the Roman Republic: the tribunes of the plebs were granted sacrosanctitas, meaning any violence against their person carried the weight of a sacred, capital offence — a legal mechanism, not a figure of speech. Cassius Dio’s own writing had to work to translate the term faithfully from Latin into Greek, evidence that its precise legal force didn’t map cleanly onto informal ideas of “respected” or “esteemed.”
Modern usage has drifted toward exactly the vaguer meaning the Roman term resisted — “sacrosanct” now often just means “treated as beyond criticism,” stripped of the specific legal machinery that gave the original word its force.
Source: Freyburger-Galland, M-L. “Cassius Dio and the Sacred,” Acta Antiqua Academiae Scientiarum Hungaricae, 2021.