Acathistus

Acathistus (ἀκάθιστος, not-seated), a hymn of the Greek Church sung on the eve of the fifth Sunday in Lent in honor of the Blessed Virgin; so called because during the singing of it the whole congregation stood, while during the singing of other hymn of the same kind they occasionally sat. Its origin has been assigned more especially to the deliverance of Constantinople from Chosroes, king of the Persians, in the reign of the emperor Heraclius, A.D. 626.