During his battle with Set to avenge the murder of his father, Osiris, Horus' eye was plucked out and torn apart. After his victory, the eye was pieced together by Thoth who added a small bit of magic to make up for the 1/64th of a piece that was
missing.
The symbol was a powerful amulet. The eye was painted on boats and other objects in need of divine protection. Jewelled copies of the eye were placed with the dead and painted on sarcophagi. Also called the Udjat or sound eye, the symbol originally belonged to Maat, goddess of truth. As the regenerated Eye of Horus, it was worn to ensure good health.
An eye within a triangle pyramid is a variation popularised by Freemasonry. It represented the eye during Horus' time in the underworld awaiting rebirth. It appears on the Great Seal of the United States and on the US dollar bill, evidence of the influence that Freemasonry had during the formation of the county.