The Octagon was a burial chamber dome on a rectangular base, containing the body of a woman of 15 or 16 years old, in a marble sarcophagus. According to interpretations it is a monument and tomb of Ptolemy Arsinoe IV, the younger sister of the famous Cleopatra VII, who was murdered in Ephesus in the year 41 B.C.
Arsinoe IV was the fourth daughter of Ptolemy XII Auletes, sister of Ptolemy XIII and Cleopatra VII, and one of the last rulers of the Ptolemaic Dynasty of Ancient Egypt. When the father died, he left Ptolemy and Cleopatra as joint rulers of Egypt, but Ptolemy soon dethroned Cleopatra and forced her to run away from Alexandria.
When Julius Caesar arrived in Alexandria in 48 B.C. and sided with Cleopatra’s faction, Arsinoe escaped from the capital with her mentor Ganymede and joined the Egyptian army under Achilles, assuming the title of pharaoh. But facing Achilles and Ganymede, Arsinoe commanded to kill the soldier and putted her mentor over the army. Ganymede initially managed to achieve some success against the Romans, negotiating an exchange of Arsinoe by Ptolemy, but the Romans soon received reinforcements and inflicted a decisive defeat on the Egyptians.
Arsinoe was transported to Rome, where she was forced to appear in Caesar’s victory. Despite the tradition of strangling prisoners at the end of the holidays, Caesar forgave Arsinoe’s life and sent her to a sanctuary of Ephesus. Arsinoe lived in the temple for many years, always cautious of the attitude of her sister Cleopatra, who saw her as a threat to the power. Her fears were well founded and in 41 B.C., at the initiative of Cleopatra, Mark Antony ordered the execution of the younger sister on the steps of the temple. She was given a funeral and a modest honorable grave.