
"Ū" is a separate letter but given the same position in collation as the unaccented "u". Ō was also used in Latvian, but it was discarded as of 1957. "Ā", "ē", "ī", "ū" are separate letters that sort in alphabetical order immediately after "a", "e", "i", "u" respectively.

Slavicists use the macron to indicate a non-tonic long vowel, or a non-tonic syllabic liquid, such as on l, lj, m, n, nj, and r.The following languages or transliteration systems use the macron to mark long vowels: Though many textbooks about ancient Rome and Greece employ the macron, it was not actually used at that time. 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.

In Greco-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.
