Etymologiae, Book I, chapters 15-17: De litteris apud grammaticos to De pedibus
Chapter XV. On letters among the grammarians How many articulate sounds there are. And the letter (littera) is so called as if legitera, because it furnishes a way (iter) for those who read, or because it is repeated (iteretur) in reading.
Chapter XVI. On the syllable The syllable is called in Greek, in Latin conceptio or complexio. For syllaba is named from syllambanein ta grammata, that is, from the conception of letters; for syllambanein means to conceive. Hence that is truly a syllable which is born of several letters. For a single vowel is called a syllable by misuse, not properly, and is to be called not so much a syllable as a reckoning of times. Syllables are short, long or common. Short ones are so called because they can never be lengthened. Long ones, because they are always lengthened. Common ones, because at the writer’s discretion, when necessity compels, they are both lengthened and shortened. Read Donatus. Syllables are called long and short because, through the various delays of the voice, they seem to have double or single spaces of time. Diphthong syllables are so called by a Greek name, because in them two vowels are joined. Of these, among us, four are true: ae, oe, au, eu. Ei was in use only among our forebears. Among the metricians a syllable is called a semipes because it is half a foot. For a foot consists of two syllables. When there is one syllable, it is as it were half a foot. Dionysius of Lintus made for every syllable its own most fitting forms, and on that account was honoured with a statue.
Chapter XVII. On feet Feet are those which rest on fixed times of syllables and never depart from the lawful space. Feet are so called because the metres walk by them. For as we move on feet, so the metres advance as if on feet. There are in all one hundred and twenty-four feet: of two syllables four, of three syllables eight, of four syllables sixteen, of five syllables thirty-two, of six syllables sixty-four. Up to four syllables they are called feet; the rest are called syzygies. The feet themselves have special reasons for their names, why they are so called. The pyrrhic is so called because it was constantly and often used in contest or in boys’ play. The spondee is so called because it sounds drawn out. For the spondee is a kind of drawing out, that is, a sound that was poured out about the ears of those sacrificing.
Hence also those who played the pipes at the rites of the pagans were called spondial. The trochee is so called because it makes a swift turning of the song and runs quickly in the metres like a wheel. For trochos in Greek means a wheel. The iamb is so called because the Greeks said iambizein for to disparage. For poets were accustomed to fill all invectives and disparagements with verse of this kind. The name is from the fact that it pours out, in a certain way, the poison of cursing or spite. The tribrach, which is also called the choree, is called tribrach because it is made of three shorts. The molossus is named from the dance of the Molossians, which they performed armed. The anapaest is so called because this foot is more devoted to relaxations and games. The dactyl is named from the finger, because beginning from a longer joint it ends in two short ones. So also this foot has one long joint and two short ones. Hence the hand spread out is called the palm, and the hanging fingers dactyls.
The amphibrach, because it has a short at each end, with a long lying between in the middle.
For brachys means short.
The amphimacer, because the two longs on either side have a short enclosed in the middle. For makros means long. The bacchius is so called because with that foot the Bacchic rites, that is, the rites of Liber, were celebrated.
The antibacchius or palimbacchius is so called because it is a repetition of the bacchius. The proceleusmatic, because it is fit for those singing the celeuma.
The dispondee, the ditrochee and the diiamb are so called because they consist of double iambs, spondees or trochees.
The antispast, because it is made of contrary syllables, of a short and a long, of a long and a short. The choriamb, because a song composed of this foot is most fitting for choruses. The Ionics are so called on account of the unequal sound of their numbers. For they have two long syllables and two short. The paeons are named from their inventor. They consist of one long and three shorts, and the long is placed variously according to their names. The epitrites are so called because they always have three long syllables and one short. Syzygies are the feet of five and six syllables; and among the Greeks they are called syzygiai, as a kind of declensions. But these are not feet, but are called pentasyllables and hexasyllables, because they do not proceed beyond five and six syllables. Hence it is not fitting in a verse that these syllables exceed any name whatever, as Carthaginiensium, Hierosolymitanorum and Constantinopolitanorum. To each foot belong arsis and thesis, that is, the raising and the setting down of the voice. For feet cannot direct their course unless they are raised and set down in alternate turn, as in arma: ar is the raising, ma the setting down. In these two the lawful feet are gathered by division. The division is equal whenever the arsis and thesis are cut in an equal division of times. Double, whenever one of them exceeds the other by double. Sescuple, whenever one exceeds the other by a sescuple. For in the single part of it one more is found; in the double, one less is held. For sescum means half. Triple is when the greater part contains the whole of the less three times, that is, three and one.
Epitrite is when the less is contained by the greater, together with a third part of it. The members of feet are divided either by equality or by the double or by the sescuple or by the triple or by the epitrite. We divide equally, then, these: the spondee, the pyrrhic, the dactyl, the anapaest, the dispondee, the proceleusmatic, the diiamb, the ditrochee, the antispast, the choriamb. Likewise we divide in the double these feet: the trochee, the iamb, the molossus, the tribrach, the greater Ionic, the lesser Ionic. There is only one that is divided by the triple division, which is the greatest and therefore is found in the smallest metres: the amphibrach. The sescuple are these: the amphimacer, the bacchius, the antibacchius, the first paeon, the second paeon, the third paeon, the fourth paeon. There remain those which we divide by the epitrite division: the first epitrite, the second epitrite, the third epitrite, the fourth epitrite. There are, therefore, ten equal, six double, one triple, seven sescuple, four epitrite.
There is only one that is divided by the triple division, which is the greatest and therefore is found in the smallest metres. The number of syllables in feet extends from two to six; for it does not go beyond, because feet are stretched up to six syllables. The times in feet are how many each foot has. Resolution of feet is when two shorts are put for one long, or four shorts for two longs, as: “and they weave the ribs with fir-wood sides.” Here abiete is a resolution of the spondee into a proceleusmatic, in which resolution Virgil always follows synaloepha. From one long two shorts are made; but from two shorts a long is never made. For solid things can be split, but split things cannot be made solid. The figure is that by which the marks of syllables are recognized. For where you see the lower part of a circle placed twice, it is a pyrrhic; where a double line lying down, a spondee. For the mark of a short is a lower semicircle; the mark of a long is a lying line. Metres arise from the feet, as the trochaic from the trochee, the dactylic from the dactyl, the iambic from the iamb, of which we shall speak a little later.