A metron , (from ancient Greek "measure"), plural metra, is a repeating section, 3 to 6 syllables long, of a poetic metre. The word is particularly used in reference to ancient Greek. According to a definition by Paul Maas, usually a metron consists of two long elements and up to two other elements which can be short, anceps or biceps.
Thus an iambic metron is x – ᴗ – (where "x" represents an anceps element), a trochaic metron is – ᴗ – x, an ionic metron is ᴗ ᴗ – –, an anapaestic metron is ᴗᴗ – ᴗᴗ –, a cretic metron – ᴗ –, a baccheus is ᴗ – –, and a spondee is – –.
This definition of the metron (i.e. as having two long elements) does not apply to the dactylic hexameter or to the dochmiac metre, but some scholars regard the dactyl (– ᴗᴗ) and the dochmiac (ᴗ – – ᴗ –) as metra in their own right. Some of the more complex lyric metres, such as the dactylo-epitrite used in some of Pindar's odes, are not usually analysed in terms of metra.
Some metra, such as the iambic x – ᴗ – or the trochaic – ᴗ – x, can be analysed as consisting of two "feet". In this case the metron is also sometimes known as a "dipody" , from ancient Greek .
"Metron" in ancient Greek
In ancient Greek, the word had a variety of meanings. The basic meaning is the "measure, size, length" of something. Another meaning is "metre" or "verse", for example () "putting words into verse" (Plato); a is an expert in metre. () in Aristotle means "the iambic metre". But Aristotle also defines as () "parts of the rhythms".
Ancient prosodists such as Hephaestion referred to metra using individual names for the different shapes: thus Hephaestion refers to the shape ᴗ ᴗ – ᴗ as the "third paeonic" and – ᴗ – – as the "second epitrite" and so on.
The words "dimeter", "trimeter" and "tetrameter" are found in ancient Greek.
Other names
The equivalent of metra can also be found in the poetry of other languages, such as Arabic, Persian, and Sanskrit. However, in descriptions of the metres of these languages, what in Greek metrics is called a "metron" (i.e. a repeating section of 3 to 6 syllables) is often called a "foot".
Thus in the traditional description of Arabic metre by William Wright, a section such as – – ᴗ – is referred to as a "foot"; but Golston and Riad refer to it as a "metron": "A crucial element of our analysis is that what is traditionally considered a verse foot is in fact a metron (two verse feet)."
Similarly Bruce Hayes and Finn Thiesen refer to a four-syllable repeating section of a Persian metre as a "foot". Despite using the term "foot", both Wright and Hayes refer to lines with two, three or four feet respectively as dimeters, trimeters and tetrameters.
Trimeters and tetrameters
A line of poetry most commonly consists of from two to four metra, rarely of a single metron. The terms "monometer", "dimeter", "trimeter", and "tetrameter" are used for metres that consist of one, two, three, or four metra respectively.
Thus an ancient Greek iambic trimeter has the following pattern:
x – ᴗ – | x – ᴗ – | x – ᴗ –
A dactylic hexameter, however, has six feet, not six metra, since according to Paul Maas's definition a dactylic metron (as used in lyric poetry) is – ᴗᴗ – ᴗᴗ.
Normally in Greek and Latin, in those metres where a metron is defined as having two long elements, there are no more than four metra in any line of poetry. There are rare exceptions such as Callimachus fragment 399 (trochaic pentameter catalectic) and fragment 229 (a choriambic pentameter).
The same rule also applies in Arabic and Persian. Thus in Wright's list of Arabic metres, there are dimeters, trimeters, and tetrameters only, and similarly in Persian, no metre is longer than a tetrameter of 16 syllables, or shorter than 10 syllables.
In some kinds of Greek and Latin lyric poetry, however, the same type of metra may run on without stopping for a number of lines with no pause at the end of each line. Such passages are known as "systems" and can be found in trochaic, ionic, and anapaestic metres.
Catalexis
In some cases the last element of a metre is omitted. In this case the metre is called "catalectic". For example, the following metre is known as a trochaic tetrameter catalectic (in Latin it is known as a trochaic septenarius):
– ᴗ – x | – ᴗ – x | – ᴗ – x | – ᴗ –
If an iambic metre ending in a long element is made catalectic, the final metron changes from x – ᴗ – to ᴗ – x (with brevis in longo at the end). For example, the iambic tetrameter catalectic is as follows: