The O Antiphons are chanted during Vespers in Advent. They were in use no later than the eighth century, and possibly as early as the sixth.
I made a photo series that, for each image, combines one of the antiphons with one quotation from Dom Prosper Gueranger's The Liturgical Year. I have also added manuscripts from a variety of European places and centuries, illuminating how the O Antiphons have been sung and written throughout our Catholic history.
I am greatly indebted to the Cantus Database for indexing so many beautiful manuscripts.
Manuscript: University of Michigan Library, Antiphonal B3971321 (15th century). http://quod.lib.umich.edu/s/sclib/x-b3971321/28863_0009
Manuscript: Latrobe University Library, Poissy Antiphonal (14th century). https://www.lib.latrobe.edu.au/MMDB/images/Poissy/FOL_001R.htm
Manuscript: Digital Library of University of Wroclaw, oai:bibliotekacyfrowa.pl:24562, Antiphonarium (14th century). https://glam.uni.wroc.pl/index.php?s=RKP_I_F_401_23465&p=24&x=0.4107585605854048&y=0.36429170882177264&z=0.6087723944973988&browser=seadragon
Manuscript: Münchener DigitalisierungsZentrum, MA Impr. 1537, Antiphonarium (16th century). https://daten.digitale-sammlungen.de/0009/bsb00090351/images/index.html?fip=184.108.40.206&id=00090351&seite=50
Manuscript: Bibliothèque Nationale de France, ark:/12148/btv1b84262784, Antiphonaire (13th century). https://gallica.bnf.fr/ark:/12148/btv1b84262784/f36.image
Manuscript: Bibliothèque Nationale de France, ark:/12148/btv1b10033588d, Antiphonaires (12th century), https://gallica.bnf.fr/ark:/12148/btv1b10033588d/f23.image
Manuscript: Badische Landesbibliothek, Cod. Aug. perg. 60, Antiphonarium (12th century). https://digital.blb-karlsruhe.de/blbhs/content/pageview/1253202