A longa is a musical note that could be either twice or three times as long as a breve

Double whole note

In music, a double whole note or breve is a note lasting twice as long as a whole note...

, four or six times as long as a semibreve/whole note, that appears in early music

Early music

Early music is generally understood as comprising all music from the earliest times up to the Renaissance. However, today this term has come to include "any music for which a historically appropriate style of performance must be reconstructed on the basis of surviving scores, treatises,...

. It is no longer used in modern

Modern musical symbols

Modern musical symbols are the marks and symbols that are widely used in musical scores of all styles and instruments today. This is intended to be a comprehensive guide to the various symbols encountered in modern musical notation.- Lines :- Clefs :...

 music notation because it cannot fit into a measure of any commonly used meter, although the sign for the equivalent rest

Rest (music)

A rest is an interval of silence in a piece of music, marked by a sign indicating the length of the pause. Each rest symbol corresponds with a particular note value:The quarter rest may also be found as a form in older music....

 is sometimes used to mark multi-measure rests.

Rare, but historical, is the duplex longa, called maxima in the 14th century, which is an effective "octuple whole note." As the name suggests, it was always equal to two longæ, never to three, though in the early Ars nova

Ars nova

Ars nova refers to a musical style which flourished in France and the Burgundian Low Countries in the Late Middle Ages: more particularly, in the period between the preparation of the Roman de Fauvel and the death of the composer Guillaume de Machaut in 1377...

 there was a corresponding modus maximarum which could be either imperfect (containing two longæ) or perfect (containing three longæ, or one longa plus one duplex longa) (Apel 1961, 328). In some early sources the duplex longa has the twice the body of a longa, but more often there is no clear difference of shape and the presence of the duplex longa is instead merely suggested by a greater distance between the notes in the tenor (in score notation), caused by the greater number of notes in the upper parts (Apel 1961, 224, 245). See Mensural notation

Mensural notation

Mensural notation is the musical notation system which was used in European music from the later part of the 13th century until about 1600."Mensural" refers to the ability of this system to notate complex rhythms with great exactness and flexibility...

for examples.