Actually, Amanda, I think I said those lines from Robert Frost were hendecasyllabics , not hexameters . Or I may have misspoken. Regardless, hendecasyllabic they are, the eleven-syllable line passing into English ultimately from Latin.

Here, for example is the meter of Horace’s alcaic stanza in Latin poetry:

x — u — — ^^ — u u — u x
x — u — — ^^ — u u — u x
x — u — — — u — x
— u u — u u — u — x

(Where “—” means a long syllable, “u” a short, and “x” either, and “^^” means the caesura.)

Translated into stresses, with a trochee substituted for the spondee, that makes it in English:

x / v / v / v v / v x
x / v / v / v v / v x
x / v / v / v / x
/ v v / v v / v / x

The first two lines here are hendecasyllabics. Such eleven-syllable lines have a strong life in Italian—in Dante, for instance—where they are very flexible and where rules have emerged to keep track of the dactyl and the number of stresses.

Still, there’s a difference in the ways these hendecasyllabic lines are used in English. One can speak here of asclepiads, first, second, etc., but an easier way to think of it might be this: The hendecasyllabic line in narrative poetry wants the two unstressed syllables to come early, the opening two hendecasyllabic lines in an alcaic want them to come late.

The example you cite, Robert Frost’s “For Once, Then, Something,” is a fine example of narrative hendecasyllabics. What’s amazing, I think, about this poem is that it sounds unstrained, but every line is exactly regular: /v/vv/v/v/v.

Others taunt me with having knelt at well-curbs
/v/vv/v/v/v
Always wrong to the light, so never seeing
/v/vv/v/v/v
Deeper down in the well than where the water
/v/vv/v/v/v
Gives me back in a shining surface picture
/v/vv/v/v/v
Me myself in the summer heaven godlike
/v/vv/v/v/v
Looking out of a wreath of fern and cloud puffs.
/v/vv/v/v/v

Tennyson’s “Hendecasyllabics” is perhaps even more amazing, though much more artificial, for Tennyson has tried to line up long syllables (so the poem is accurate in quantity) with the stresses:

O you chorus of indolent reviewers,
/v/vv/v/v/v
Irresponsible, indolent reviewers,
/v/vv/v/v/v
Look, I come to the test, a tiny poem
/v/vv/v/v/v
All composed in a metre of Catullus,
/v/vv/v/v/v
All in quantity, careful of my motion,
/v/vv/v/v/v
Like the skater on ice that hardly bears him
/v/vv/v/v/v

In the two hendecasyllabic lines that open an alcaic stanza, however, the dactyl typically comes later in the line, not as the second foot but after the caesura: not /v/vv/v/v/v but x/v/v/vv/vx. So, for example, here are the opening two lines of Robert Louis Stevenson’s “Alcaics: to H. F. B.”

Brave lads in olden musical centuries
//v/v/vv/vv
Sang, night by night, adorable choruses,
//v/v/vv/vv

And here are the opening two lines of Tennyson’s “Milton: Alcaics” (again a tour-de-force, trying to line up quantity and stress):

O mighty-mouth’d inventor of harmonies,
//v/v/vv/vv
O skill’d to sing of Time or Eternity,
//v/v/vv/vv

Here’s the beginning of Arthur Hugh Clough’s “Alcaics”:

So spake the voice: and as with a single life
//v/v/vv/vx
Instinct, the whole mass, fierce, irretainable,
//v/v/vv/vx

It’s interesting that these Victorian examples all attempt the difficult task of forcing a spondee to begin each line. Edwin Arlington Robinson’s “Late Summer” doesn’t attempt that (although I think he may “hear” it in some way, thickening that opening foot with a hint of quantity):

Confused, he found her lavishing feminine
v/v/v/vv/vv
Gold upon clay, and found her inscrutable;
/vv/v/vv/vv

As this example shows, there’s plenty of room for substitution in the first few feet, but that dactyl in the penultimate position seems to me the defining feature of the hendecasyllabic line in an alcaic stanza.

More recent poets have treated the opening two lines of the alcaic stanza in English as almost genuine “syllabic” lines: carrying any metrical pattern that sounds good, as long as it has eleven syllables. W.H. Auden’s “In Memory of Sigmund Freud” are alcaics that will sometimes use the traditional pattern:

Only Hate was happy, hoping to augment
/v/v/v/vv/v

but often Auden will vary this wildly, to great effect:

For about him till the very end were still
/v/v/v/v/v/
those he had studied, the fauna of the night,
/vv/vv/v/v/

Regardless, after the opening eleven-syllable lines, the alcaic stanza adds two more, a nine-syllable line and a ten-syllable line. At an early stage in Greek, these were apparently one nineteen-syllable line, but by the time they reach the Romans, it is routine to hear them as two lines (so Horace, for example, will admit hiatus between them).

x/v/v/v/x
/vv/vv/v/x

To use the same examples as above, here’s Stevenson’s “Alcaics: to H. F. B.”:

Brave lads in olden musical centuries
Sang, night by night, adorable choruses,
Sat late by alehouse doors in April
Chaunting in joy as the moon was rising.

These final lines run //v/v/v/v and /vv/vv/v/v. Tennyson’s “Milton: Alcaics” is precisely the same:

O mighty-mouth’d inventor of harmonies,
O skill’d to sing of Time or Eternity,
God-gifted organ-voice of England,
Milton, a name to resound for ages;

These end with //v/v/v/x and /vv/vv/v/x, as do Clough’s “Alcaics”:

So spake the voice: and as with a single life
Instinct, the whole mass, fierce, irretainable,
Down on that unsuspecting host swept;
Down, with the fury of winds, that all night

Robinson’s “Late Summer” drops the attempt to have a spondee open the third line, but otherwise uses the same pattern for the last two lines, v/v/v/v/x and /vv/vv/v/x:

Confused, he found her lavishing feminine
Gold upon clay, and found her inscrutable;
And yet she smiled. Why, then, should horrors
Be as they were, without end, her playthings?

These, then are the two main uses of hendecasyllabic lines in English: As a straight-forward narrative line, with the substitution typically in the second foot, and as the opening of an alcaic stanza, with the substituted dactyl typically coming later in the line.

More information than you need, Amanda, to appreciate the Frost poem , I know, but there it is.