This article is a fragment taken from the longer article on Amazons.

The twelfth of the famous Labors of Hercules was to obtain the girdle of Hippolyta, Queen of the Amazons, by negotiation or by force.

Hippolyta was gracious and gave Hercules the girdle freely.  However, Juno, acting on her unceasing vindictiveness against Hercules, disguised herself as an Amazon and put it about that Hercules was stealing the girdle.  The Amazons attacked the visiting heroes; Hercules believed he had been betrayed and slew Hippolyta.