One of the special uses of amulets was for seafaring people, for, in ancient times especially, all who went down to the sea in ships were greatly in need of protection from the fury of the elements when they embarked in their small sailing-vessels. A fragment of a Greek Lapidary,[23] probably written in the third or fourth century of our era, gives a list of seven amulets peculiarly adapted for this purpose. The number might suggest a connection with the days of the week, and the amulets were perhaps regarded as most efficacious when used on the respective days. In the first were set a carbuncle and a chalcedony; this amulet protected sailors from drowning. The second had for its gem either of two varieties of the adamas,—one, the Macedonian, being likened to ice (this was probably rock-crystal), while the other, the Indian, of a silvery hue, may possibly have been our corundum; however, the Macedonian stone was regarded as the better. The third amulet bore the beryl, “transparent, brilliant, and of a sea-green hue,” evidently the aquamarine beryl; this banished fear. The fourth had for its gem the _druops_, “white in the centre,” probably the variety of agate so much favored as a protector against the spell of the Evil Eye. A coral was placed in the fifth amulet, and this was to be attached to the prow of the ship with strips of seal-skin; it guarded the vessel from winds and waves in all waters. For the sixth amulet the _ophiokiolus_ stone was selected, most probably a kind of banded agate, for it is said to have been girdled with stripes like the body of a snake; whoever wore this had no need to fear the surging ocean. The seventh and last of these nautical amulets bore a stone called _opsianos_, apparently a resinous or bituminous material, possibly a kind of jet; this came from Phrygia and Galatia, and the amulet wherein it was set was a great protection for all who journeyed by sea or by river. The ancient treatises on the magic art show that the use of amulets was considered to be indispensable for those who dared to evoke the dark spirits of the nether-world, for without the protection afforded by his amulet the magician ran the risk of being attacked by these spirits. One of these texts gives directions for preparing an amulet, or _phylacterion_, for the “undertaking”; for this a “sweet-smelling” loadstone should be chosen, and should be cut heart-shaped and engraved with the figure of Hecate.[24]