https://tinyurl.com/ASolisOrtus

A poem written more than 1500 years ago, this is one of the oldest known Catholic hymns. It recounts the story of Jesus from his Birth through his Ascension. Each of the 23 verses begins with the next letter of the Roman alphabet. This kind of poem is called an abecedarius, and it’s a type of acrostic. The earliest known abecedaria are from the Bible, and if you attend Tenebrae during Holy Week you’ll hear the Lamentations of Jeremiah, in which each letter of the alphabet is actually sung before the corresponding line, just to highlight this fact, which is pretty cool.

The first 7 verses are used as a hymn for Lauds during Christmas season, and another 4 verses (Hostes Herodies Impie) are sung at Epiphany.

The whole poem is too long to fit into this description, so here's a link to the lyrics --

https://tinyurl.com/ASolisOrtusText