The Octagon is another link between Ephesus and Egypt. It was a vaulted burial chamber placed on a rectangular pedestal. This chamber housed the skeleton of a fifteen or sixteen year old woman in a marble sarcophagus. According to an interpretation, this structure was a monument to the youngest sister of Cleopatra, Ptolemy Arsinoe IV, who was murdered in the city of Ephesus in 41 BC. This murder was possibly ordered by the victim’s own sister to avoid the potential for Arsinoe to be the next queen of Egypt. It is thought that Arsinoe was poisoned by Cleopatra with Arsenic. Thus, the poison may have been given its name from the murdered Egyptian princess.

Arsinoe IV was one of the last rulers of the Ptolemaic dynasty of ancient Egypt. When the king died he left Ptolemy and Cleopatra to jointly rule Egypt, but Ptolemy soon dethroned Cleopatra and forced her to flee Alexandria. Caesar arrived in Alexandria in 48 BC and sided with Cleopatra, forcing Arsinoe to flee from the capital with her mentor Ganymedes. Taking the title of pharaoh, Arionoe joined the Egyptian army under Achillas, but had the general killed when he clashed with Ganymedes. Her mentor assumed charge of the army and initially enjoyed some success, the Romans soon received reinforcements and eventually defeated the Egyptian army.

Arsinoe was brought to Rome and forced to take part in the celebration of Caesar’s triumph. Caesar spared Arsinoe the usual tradition of prisoners being strangled at the end of festivities.  Instead he granted her sanctuary at Ephesus where Arsinoe lived in the temple for many years. The younger royal was aware that her sister Cleopatra viewed her as a threat to power. She was ordered to be executed on the steps of the temple by Mark Antony at Cleopatra’s instigation.

Arsinoe was granted an honorable funeral and the octagon served as her modest tomb.