I always was fascinated by the elegiac couplet. It's a line of dactylic hexamater

BAM ba ba BAM ba ba BAM ba ba BAM ba ba BAM ba ba BAM BAM

(with all the usual trochaic substitutions, of course, and where BAM is a long and ba is a short)

alternating with what they call a pentameter but which is really not a pentamter at all

BAM ba ba BAM ba ba BAM // BAM ba ba BAM ba ba BAM

Why does this line combine so well with the other? Well there is often a Caesura in the middle of the third foot of the DH line:

BAM ba ba BAM ba ba BAM / ba ba...

[e.g. Arma virumque cano...]

So you take that part of the DH line, before the ceasura, and it becomes half of the so-called "pentameter," or 2.5 metrical feet. It's a great asymmetrical feel, beloved of Catullus and Ovid, not to mention Propertius. Elegiacs: not just for elegy.

The shorter "pentameter" line wouldn't really work by itself, I don't think. The DH does work as its own meter, of course, but elegiac couplets are much hipper. I love that feeling of "coming up short" in the second line.

Multas per gentes et multa per aequora vectus
advenio has miseras, frater, ad inferias.