Of this sort is the main story of an epic poem, "The return of Ulysses, the settlement of the Trojans in Italy," or the like.
That of the Iliad is the "anger of Achilles," the most short and single subject that ever was chosen by any poet.

Yet this he has supplied with a vaster variety of incidents and events, and crowded with a greater number of councils, speeches, battles, and episodes of all kinds, than are to be found even in those poems whose schemes are of the utmost latitude and irregularity.

The action is hurried on with the most vehement spirit, and its whole duration employs not so much as fifty days.

Virgil, for want of so warm a genius, aided himself by taking in a more extensive subject, as well as a greater length of time, and contracting the design of both Homer's poems into one, which is yet but a fourth part as large as his.
The other epic poets have used the same practice, but generally carried it so far as to superinduce a multiplicity of fables, destroy the unity of action, and lose their readers in an unreasonable length of time.

Nor is it only in the main design that they have been unable to add to his invention, but they have followed him in every episode and part of story.
If he has given a regular catalogue of an army, they all draw up their forces in the same order.