This is yet another of those poems that was preserved in monastic manuscripts. It is a brief one.

Ron-bris
Ron-brúi
Ron-báid
a Rí in ríchid rindglaine

Ron-geilt in gáeth feib geiles
nemáed forderg fidnaige

This verse caught the attention of those German-born philologists who specialized in Gaelic during the 1800's and laid an academic foundation for the students of older forms of Gaelic who followed them, amongst others Dr. Kuno Meyer. Naturally a German translation was the result. This is the best I can make out of the German translation.

We have been broken
We have been crushed
We have been drowned
O King of the kingdom bright as the stars

We have been consumed by the wind
as is consumed
kindling
by the crimson fire of lightning from the sky

What seems to have happened, is that when Gaelic was taught long ago, this little verse was taken out of whatever context/origin, and isolated for study in a Glossary. This Glossary is itself centuries old, and the entire student's Glossary, in the old Gaelic, is embedded in later manuscripts. Thus the verse was preserved until the 19th-century philologists and linguists could uncover it.

The mystery of course is where this might have come from in the first place; and I rather fear it will never be known. What are the odds of discovering this archaic Irish verse, not isolated for analysis in a Glossary, but within some larger literary work that would provide context? Will we ever know what this verse is about?

In English translation (different from the above) this has been set to music by Samuel Barber in the 20th century, in his Hermit Songs.