Crotalum

In classical antiquity, a crotalum (κρόταλον krotalon)[2] was a kind of clapper or castanet used in religious dances by groups in ancient Greece and elsewhere, including the Korybantes.

[5] From the Suda and the Scholiast on Aristophanes (Nubes, 260), it appears to have been a split reed or cane, which clattered when shaken with the hand.

Clement of Alexandria attributes the instruments invention to the Sicilians, and forbids the use thereof to the Christians, because of the motions and gestures accompanying the practice.

Such was Virgil's Copa (2), This line alludes to the dance with crotala (similar to castanets), for which we have the additional testimony of Macrobius (Saturnalia III.14.4‑8).

[7] Pausanias affirms by way of the epic poet Pisander of Camirus that Heracles did not kill the birds of Lake Stymphalia, but that he drove them away by playing on crotala.

Illustration taken from the drawing of an ancient marble in Spon 's Miscellanea , [ 1 ] representing one of the crotalistriae performing.
Afterlife scene of a woman playing crotalum clappers leading a man playing a barbitos lyre.