The belief that some persons had the power of injuring others by their looks, was as prevalent among the Greeks and Romans as it is among the superstitious in modern times. The ὀφθαλμὸς βάσκανος, or evil eye, is frequently mentioned by ancient writers. It was supposed to injure children particularly, but sometimes cattle also.
Various amulets were used to avert the influence of the evil eye. The most common of these appears to have been the phallus, called by the Romans fascinum, which was hung round the necks of children. Pliny also says that Satyrica signa, by which he means the phallus, were placed in gardens and on hearths as a protection against the fascinations of the envious; and we learn from Pollux that smiths were accustomed to place the same figures before their forges with the same design.
Sometimes other objects were employed for this purpose. Peisistratus is said to have hung the figure of a kind of grasshopper before the Acropolis as a preservative against fascination Another common mode of averting fascination was by spitting into the folds of one's own dress.
According to Pliny, Fascinus was the name of a god, who was worshipped among the Roman sacra by the Vestal virgins, and was placed under the chariot of those who triumphed as a protection against fascination; by which he means in all probability that the phallus was placed under the chariot.
From: A Dictionary of Greek and Roman Antiquities, John Murray, London, 1875.