A macron, from the Greek μακρόv (makrón), meaning "long", is a diacritic placed above a vowel (and, more rarely, under or above a consonant). It was originally used to mark a long syllable in Græco-Roman metrics, but now also indicates that the vowel is long. (This is the opposite of a breve ˘, used to indicate originally a short syllable and now also a short vowel.) Distinctions between long and short vowels are often phonemic. In the International Phonetic Alphabet the macron is used to indicate mid tone; the sign for a long vowel is a modified triangular colon.

Syllable weight

In Græco-Roman metrics and in the description of the metrics of other literatures, the macron was introduced and is still widely used to mark a long (i.e., heavy) syllable. Even the best and relatively recent classical Greek and Latin dictionaries are still only concerned with indicating the length (i.e., weight) of syllables; that is why most still do not indicate the length of vowels in syllables that are otherwise metrically determined. Though many textbooks about ancient Rome and Greece employ the macron, it was not actually used at that time.