Note: I think this is a replica of the Divje Babe Flute, thought to be the oldest known musical instrument in the world. Some researchers think it was made by Neanderthals, but that's still up in the air, apparently.
"The ancient Celts had a distinct culture, which is shown by their very sophisticated art work. The Hallstatt culture and especially the later La Tène culture are characterized by a high aesthetic level, which must have also left traces in ancient Celtic music." Source: Citizendium.
Note: The video shows the Welsh Crwth, aka "The Fiddle of the Welsh Bards." The music, like most modern versions of ancient music, is an improvisation and may or may not be historically accurate.
Notes: Parts 2 and 3 can be found here. Music is composed and performed by Synaulia, "a team of musicians, archeologists, paleorganologists and choreographers dedicated to the application of their historical research to ancient music and dance, in particular to the ancient Etruscan and Roman period," according to Wikipedia.
The Romans apparently didn't write their music down, so these are modern compositions, the result of research and presumably a lot of guesswork. According to the Synaulia web page, "in the absence of a system of musical notation for the period in question, the reconstruction and study of ancient musical expression was based on comparative studies of iconography, textual analysis, social studies and customs, also drawing from paleorganology, ethnomusicology, archaeology and historiography."
"Thousands of years after they resonated in caves, two dozen stone chimes used by our prehistoric forefathers will make music once more in a unique series of concerts in Paris." Source: Archaeology News Network.
"Known as lithophones, the instruments have been dusted off from museum storage to be played in public for the first time to give modern Man an idea of his ancestral sounds."
Note: There will only be three concerts, I think. Four percussionists will be playing a piece called PaleoMusique written by composer Philippe Fenelon.
"We will never repeat it, for ethical reasons—to avoid damaging our cultural heritage. We don't want to add to the wear of these instruments," according to a music archaeologist involved in the project.
Comment: I have to wonder if these "stone chimes" are really musical instruments. They date back to 8000-2500 BC and were originally thought to have been used for grinding grain, which seems like a more plausible explanation to me. Their musical nature was discovered when an archaeologist started tapping on them, but think about all the modern objects that make xylophone-like sounds when you tap on them. Glass bottles, for instance. If some future archaeologist digs up a huge collection of bottles, maybe he'll think they were musical instruments as well.