What is the form that Aristotle described as an action of high importance?

Tradgedy

"A tragedy, then, is the imitation of an action that is serious and also, as having magnitude, complete in itself; in language with pleasurable acces­sories, each kind brought in separately in the parts of the work; in a dramatic, not in a narrative form; with in­cidents arousing pity and fear, wherewith to accomplish its catharsis of such emotions." (Imgram Bywater: 35). "Tragedy, then, is an imitation of an action of high importance, complete and of some ampli­tude; in language enhanced by distinct and varying beauties; acted not narrated; by means of pity and fear effectuating its purgation of these emotions."