The dactyl serves as the basic rhythmic unit, or metron, of hexameter verse. The word hexameter also derives from Greek and essentially means "six metrons (or, to be precise, metra) in a row."  In other words, a single epic verse consists of six successive dactyls, as Figure B shows.

Observe that the final metron is technically not a dactyl.   Its second syllable is called the anceps (Latin for "two-headed"), which is noted either as  or .  No hexameter verse ends in ;  in its place one finds the anceps, which is either short or long—it does not matter.  In fact, for purposes of recitation, the anceps is always treated as long to fill out the line.

A more common word for metron is foot, the idea behind this term being that a line of metra marches past one's ear during recitation.  The long syllable, which is the first half of the foot, is called the thesis (Greek for "putting down") because the foot is imagined as touching the ground;  the two short syllables are therefore called the arsis (Greek for "lifting up"), the half in which the foot is raised up...for the next "footstep."