Chorus, among the ancients, meant a band of singers and dancers employed on festive occasions of great pomp, and also in the performance of tragedy and comedy on the stage. The choral dances in honour of Bacchus, which superseded the earlier ones to Apollo, were by their combination with the rhythmic recitations of the Rhapsodes, the origin of the Greek tragedy. In the plays as known to us the chorus consisted of a group of persons—boys, girls, or men—who remained in front of the stage during the whole performance as spectators, or rather as witnesses. When a pause took place in the acting, the chorus either sang or spoke verses having reference to the subject represented, which served to increase the impression or sensation produced by the performers. At times the chorus seemed to take part with or against the persons in the drama, by advice, comfort, exhortation, or dissuasion. In the comedy the chorus also addressed the audience. In the time of Æschylus the chorus was very large, sometimes consisting of upwards of fifty persons, but the chorus of Sophocles numbered only fifteen. Its leader was termed the Coryphæus. The charge of organising it was considered a great honour among the citizens of Athens. The person appointed for this purpose was called the choragus. The honour was very expensive, as the choragus had to pay all the expenses incurred in training the members of the chorus to perform their parts efficiently. They were, besides, fed and lodged by him during training-time, and he had also to provide for them masks and dresses. At times the chorus was divided, and spoke or sang antiphonally. These divisions moved from side to side of the stage, from which movement originated the naming of the single songs or stanzas, such as Strophe, Antistrophe, and Epode. How the musical element of the ancient chorus was constituted or composed is not known with any certainty. It was pre-eminently founded on rhythm, the employment of which was very varied; and it was doubtless very simple. It was accompanied by flutes. With the decline of the ancient tragedy, the chorus also fell into disuse; and only lately has there been an attempt to produce the same on the stage in the manner of the ancients, as, for example, in Schiller's Bride of Messina. The music which has been set in modern times to some of the Greek tragedies does not give the least idea of the original music, which to our ears would probably sound very bare and rude. Three fragments of a Greek hymn of a late Roman period (from a Neapolitan manuscript, and the Florentine work of Galilei), which are the only extant remains of Greek music, have been transcribed in modern notation in Rowbotham's History of Music, vol. ii., and also in Chappell's History of Music, vol. i. They are of interest as being connected with the origin of the modern opera. In his later operas Wagner professes to assign to the orchestra the functions of the Greek chorus.
In modern music the word is applied to vocal pieces in which each part is intended to be sung by a considerable number of voices; and also to the body of singers who perform choral music. The number of parts may vary from unison to as many as forty or fifty; the normal number is four, but five and eight parts are also frequent. When the voices are divided into two choirs, it is called a double chorus. A chorus for both male and female voices is termed a mixed chorus. The forms of chorus are more varied than those of solo music, and the most characteristic are imitative, or contrapuntal, of which the fugue is the most regular type. They may also be in simple harmony, or a combination of the two. Choral recitative is sometimes introduced; a solo voice, or even a solo instrument, may be accompanied by chorus, or solo and chorus may answer antiphonally. A chorus sung without accompaniment is called a capella. The earliest extant form is the unisonal Plainsong (q.v.) of the Roman Church. In oratorio music, Bach's great Passion Music may be cited as containing nearly every form of chorus, from those constructed with figured parts upon a canto fermo, to the dramatic turbæ, the shouts of the enraged people. The double choruses in Handel's Israel in Egypt are also celebrated for their masterly construction and grand massive effect; and for dramatic expression those of Mendelssohn's Elijah stand in the highest rank.
In the opera as originally conceived by Peri and Caccini at the close of the 16th century, the chorus was intended to imitate that of the Greek play; and down to the time of Gluck it was arranged in two rows, without taking part in the action of the piece. Since his reforms the members of the chorus are also dramatis personæ, and sometimes, as in Auber's Masaniello, play a most important part. A definite rhythm seems essential as a means of keeping the parts together in a chorus of any length; even when Wagner, who considered rhythm 'an intruder in music,' introduces choruses, which he does but sparingly, in his operas, they are at once noticeable for this feature.
Choral singing has within the last forty years obtained a widely popular development in Britain and America, greatly owing to the publication of cheap editions of classical music. The chorus singers of Yorkshire are recognised as excelling; but it need scarcely be said that in this department of singing a very great deal of the effect depends on the conductor. A remarkable feature of the Crystal Palace Handel festivals is the gigantic body of chorus, amounting in 1888 to over 3000. See CHOIRS.