Elegiac couplet

Elegiac couplets consist of alternating lines of dactylic hexameter and pentameter?: two dactyl?s followed by a [long syllable]?, a caesura?, then two more dactyls followed by a long syllable.

Example:

  In the Hexameter rises the fountain's silvery column,
  In the pentameter aye falling in melody back.

see

Meter in poetry

Ovid