Research on the use of horns against evil/the evil eye
..We have seen how completely Isis, Artemis, and Diana were identical, and hence all three are habitually represented with the horned crescent, as their particular accompaniment or symbol: and further by the cow's head or cow's horns so often seen.
...Diana was called the "Mother of the World," strangely like the title given to the Babylonian Ishtar. The Egyptian priests styled the moon, whose personification was Isis, "The Mother of the Universe.
Domestic cattle were supposed to be under the special protection of Diana, hence we may well trace the extreme prevalence of amulets, symbolic of her attributes, upon horses. Diana was also identified through Artemis with the Greek Ilithya, the servant of Hera, and goddess of birth. She also was originally a moon-goddess, and the moon was always believed to exercise great influence on growth in general, but especially of children; so the attributes of Ilithya were passed on along with her moon-symbol, and consequently all those deities, ancient or modern, whose principal sign is the crescent, are looked upon as the special protectors of women and children against malign influence. The wearing of the crescent is a visible worship of the powerful being whose symbol it is, whether known as Isis, Parvati, Devaki, Kali, Bhavani, Artemis, Athena, Minerva, Diana or Madonna, who are all, as shown before, unam eandemque.
...Having sketched briefly the cult which may be called Isis-Diana worship, whose principal attributes were symbolised by the horned moon, we arrive at the conclusion that, to-day, horns, in one form or another, are of all objects the most common as amulets against the evil eye, whether affecting man or beast; so much so that it has at last come to be fully believed by Neapolitans that, in default of a horn of some shape in the concrete, the mere utterance of the word corno or corna is an effectual protection.
...Besides those borne on the helmet by Greeks and others, horns were worn as amulets by man and beast; so they are to this day.