They are stolen every night by Vritra the concealer, and Caecius the darkener, and Indra is obliged to spend hours in looking for them, sending Sarama, the inconstant twilight, to negotiate for their recovery. Between the storm-myth and the myth of night and morning the resemblance is sometimes so close as to confuse the interpretation of the two.
Indra, the god of light, is a herdsman who tends a herd of bright golden or violet-coloured cattle. Vritra, a snake-like monster with three heads, steals them and hides them in a cavern, but Indra slays him as Jupiter slew Caecius, and the cows are recovered.
Originally, however, the name was Caecius, "he who blinds or darkens," and it corresponds literally to the name of the Greek demon Kaikias, whom an old proverb, preserved by Aulus Gellius, describes as a stealer of the clouds. Thus the significance of the myth becomes apparent.
As Caecius, the "darkener," became ultimately changed into Cacus, the "evil one," so the name of Vritra, the "concealer," the most famous of the Panis, was gradually generalized until it came to mean "enemy," like the English word fiend, and began to be applied indiscriminately to any kind of evil spirit.