A statue of justice, also called "Lady Justice" or "Blind Justice," is commonly a woman holding a sword and scale and wearing a blindfold. She represents the legal or justice system. Lady Justice as commonly depicted in the West today is a mishmash of ancient Egyptian, Greek and Roman mythologies, likely due to the influence the mythologies had on each other over the course of the ancient empires' spread, as well as more modern concepts of justice.
In Egyptian tradition, the goddess of justice was called Ma'at. Ma'at carried a sword, as in modern depictions of justice, but instead of holding scales, she wore an ostrich feather in her hair to symbolise the same concept. Ma'at weighed the hearts of the dead to help Osiris find judgment on them. From the name "Ma'at," we get the term "magistrate."
In ancient Greek tradition, the goddess of justice is Themis, who organised human affairs and reigned over assemblies. Themis was also an Oracle at Delphi. Because she was a prophet, Themis had no blindfold, and because she represented the communal and social aspects of justice as opposed to punishment or external power, she didn't hold a sword. Another Greek contribution may include Nemesis, the personification of vengeance who was often depicted carrying a sword.
"Justitia" was the Roman goddess of justice, and like our modern depictions of justice, she was often shown wearing a blindfold and holding scales and a sword. The Roman contribution to the statue's iconography might also include the Roman representation of luck, called "Fortuna," who was often depicted as a blindfolded woman.
Blindfold, Scales and Sword
The justice statue's blindfold represents impartiality and was added to common depictions of the statue during the 15th century. Lady Justice's symbol of impartiality -- the blindfold -- reinforces the court's devotion to the objective truth. The scales represent the need to weigh the different sides of the case. The justice statue's sword is symbolic of justice's power.