1. How to scan poetry in Latin
Scanning or scansion according to dictionary.com is “to analyze (verse) as to its prosodic or metrical structure; read or recite (verse) so as to indicate or test the metrical form.”
In essence, scanning a line of poetry is to hear (and sing!) the music of the line.
It makes poetry complete. Authors are telling stories with their poems and the music is what helps the audience feel the pace, rhythm, and emotion of the verse.

2. Richard A. LaFleur, Latin Poetry for the Beginning Student, Longman, 1987, p.ix:
“…ancient poetry was composed to be read aloud (or, in certain instances, to be sung or chanted to musical accompaniment) and with the listening audience, not the reading audience, foremost in mind. The Latin poet hoped to appeal at once to the intellect and to the emotions – in varying proportion, depending upon the particular genre – and his approach to both was through the ear. Both the ‘music’ and the ‘message’ of poetry derived in part from its sound effects…When we read silently…we are neglecting altogether an important aspect of the poet’s artistry…”

3. How does it work?
The first requirement to successfully scanning poetry is to pronounce the words correctly.
Words that are pronounced with the wrong phonetic sounds can not be scanned, and therefore heard properly.
Think about all I have taught you about Latin pronunciation, listen to how I have pronounced the words for you, and you will be fine.

4. The next step is to understand the basic unit of scansion – meter.
Meter (Latin metrum, -i n. measure) is like the time signature in written music. It tells us how many feet (beats) or units (measures) of rhythm there are in the line.
Again like music, there are different meters and different arrangements of the “notes”.
The rhythm centers on whether or not the vowels in the line are long or short.
Long vowels are noted with the macron ¯ mark above them.
Short vowels are noted with the breve ̆ mark above them.

5. Quantity of vowels A vowel is said to be long in the following ways:
Long by nature:
The vowel has a long mark on it naturally. A dictionary is helpful for figuring this out if you are stuck.
There is a diphthong: ae, oe, ei, ui, au, eu
These letter combinations are marked as one syllable, not two because they make only one sound. (ae, oe, ei, ui, au, eu)
Long by position:
If the vowel is followed by a double consonant combination, the vowel is marked long. (ā, ē, ī, ō, ū)
I know it seems simplistic, but if the vowel is not long, that’s how we know it is short!

6. Elision
One key occurrence in poetry is called elision – a phenomenon which causes a vowel or sometimes a whole syllable to drop.
Elision acts like a slur does in music. It causes you to blend two syllables together that would ordinarily be separate in prose.
It is marked with a slur line: and the dropped letter is struck through with a / mark.
Elision occurs when one word ends with a vowel and the next word begins with a vowel.
Example: osculo ad This is pronounced “osculad”.
Elision also occurs when one word ends with any vowel + -m and the next word begins with a vowel.
Example: munerem ad This is pronounced “munerad”.

7. Some vowels don’t count for scansion and must be skipped over:
Caution! There are some additional idiosyncrasies about scansion that can trip you up and cause you trouble if you aren't careful!
Some vowels don’t count for scansion and must be skipped over:
The qu is regarded as one letter, not two, because the letters work together to make only one sound. Therefore the –u is not scanned.
nequiquam has only 3 vowels to scan.
The same is true for gu in situations where the –gu is pronounced with the sound of –gw. In this instance the –u is not scanned.
sanguinis has only 3 vowels to scan.
The letter h doesn’t exist as a sound therefore it does not affect scansion. Just ignore it as though it were invisible. It doesn’t count for a double consonant even if the letters before it are consonants.

8. More cautions!
The liquid consonants, r and l can really mess up your scansion and cause headaches. If there is a double consonant, and the second one in the pair is an r or an l it might be ignored in the scansion. You just have to try it and see.
Watch out for the consonantal –i. You have to remember it is acting as a consonant, so don’t try to scan it.
The letter y is always a vowel for Latin.
The letter x is only one letter physically, but it counts as a double consonant all by itself because it makes the sound of the double consonant ks.
When elision occurs between 2 words and the 2nd word is est the elision works in reverse, where the –e in est drops, not the vowel for the other word.
Example: nemo est This is pronounced “nemost”.

9. Here are some common meters and how to measure them.
Dactylic hexameter – This meter is most often used in epic poetry (a lengthy narrative poem, … concerning a serious subject containing details of heroic deeds and events significant to a culture or nation – Wikipedia).
Consists of 6 feet (hex + meter)
The most common foot is a dactyl: ¯ ̆̆ ̆
You will also have at least one spondee: ¯ ¯
The feet are marked with / between them.
The fifth foot will always be a dactyl
The sixth foot will always be a spondee

10. Let’s see an example from Ovid:
This is the first line of Ovids’ story of Pyramus and Thisbe from Book IV of the epic poem Metamorphoses.
Pyramus et Thisbe iuvenum pulcherrimus alter
When we scan it, it looks like this:
Pӯrămŭs /ēt Thīs/bē iŭvĕ/nūm pūl/chērrĭmŭs/ āltēr
To “sing” the line we take a longer time to say the syllables that are long, and a shorter time to say the syllables that are short.
Now go back to the scanned line and sing it with me!

11. When we scan the following line of Latin verse:
Hendecasyllabic
This meter consists of 11 (hendeca) syllables in 5 feet.
The feet are spondees: ¯ ¯, 1 dactyl: ¯ ̆̆ ̆, and a few troches: ¯ ̆̆ .
The feet are marked with / between them.
Example:
When we scan the following line of Latin verse:
Cui dono lepidum novum libellum
It looks like this:
Cui dō/nō lĕpĭ/dūm nŏ/vūm lĭ/bēllūm

12. Elegiac Distich (couplet)
This meter consists of one line in Dactylic Hexameter (six feet) followed by one line of Dactylic Pentameter (five feet)
The hexameter line follows the traditional pattern of dactylic hexameter with 6 feet made up of dactyls: ¯ ̆̆ ̆ and spondees: ¯ ¯.
The pentameter line is made up of 5 feet (penta), but they occur in 2 groups of 2 ½ feet.
The pentameter line consists of combinations of dactyls and spondees with 2 monosyllabic feet.
The feet are marked with / between them.
Example:
When we scan the following lines of Latin verse:
Multas per gentes et multa per aequora vectus
advenio has miseras frater ad inferias
It looks like this:
Mūltās/ pēr gēn/tēs ēt /mūltă pĕr/ aequŏră /vēctŭs
ādvĕnĭ/Ø hās mĭsĕr/ās/ frātĕr ăd/ īnfĕrĭ/ās.

13. Now it’s your turn to try
Now it’s your turn to try! Come to the board, grab a marker, and see if you can scan some lines on your own!
Arma virumque cano, Troiae qui primus ab oris
Italiam, fato profugus, Laviniaque venit
litora, multum ille et terris iactatus et alto
vi superum saevae memorem Iunonis ob iram;
multa quoque et bello passus, dum conderet urbem, 5
inferretque deos Latio, genus unde Latinum,
Albanique patres, atque altae moenia Romae.
These lines are the first sentence of Vergil’s Aeneid!
The meter is dac-tyllic hexameter

14. Here is some more practice with dactylic hexameter
Here is some more practice with dactylic hexameter! This is from Ovid’s Pyramus and Thisbe (Metamorphoses Book IV):
saepe, ubi constiterant hinc Thisbe, Pyramus illinc, inque vices fuerat captatus anhelitus oris, "invide" dicebant "paries, quid amantibus obstas? quantum erat, ut sineres toto nos corpore iungi aut, hoc si nimium est, vel ad oscula danda pateres?      75 nec sumus ingrati: tibi nos debere fatemur, quod datus est verbis ad amicas transitus auris."

15. How about these lines by Catullus:
Cui dono lepidum novum libellum
arida modo pumice expolitum?
Corneli, tibi: namque tu solebas
meas esse aliquid putare nugas
iam tum, cum ausus es unus Italorum 5
omne aevum tribus explicare cartis
doctis, Iuppiter, et laboriosis.
quare habe tibi quidquid hoc libelli
qualecumque; quod, patrona virgo
plus uno maneat perenne saeclo. 10
This is Catullus’ Poem 1
The meter is hendecasyllabic

16. This is from one of Catullus’ elegiac couplets: Poem 116
And one more.
Saepe tibi studioso animo venante requirens
carmina uti possem mittere Battiadae,
This is from one of Catullus’ elegiac couplets: Poem 116