The Philippeion (Greek: Φιλιππεῖον) in the Altis of Olympia was an Ionic circular memorial in limestone and marble, a tholos, which contained chryselephantine (ivory and gold) statues of Philip's family; himself, Alexander the Great, Olympias, Amyntas III and Eurydice I. It was made by the Athenian sculptor Leochares in celebration of Philip's victory at the battle of Chaeronea (338 BC). It was the only structure inside the Altis dedicated to a human.
The temple consisted of an outer colonnade of Ionic order with 18 columns. Inside, it had nine engaged half-columns of the lavishly- designed Corinthian order. It had a diameter of 15 metres. The naos contains two windows, much like Hera II at Paestum. It had a carved marble roof which was decorated with a bronze poppy head on top. 
The importance of the chryselephantine material used is that it was also the material used for the statue of Zeus also at Olympia (Comparing the Macedonian royal family to the gods). The fact Alexander is represented here is also important, as Philip had seven wives so after his death there very well could have been claims to the throne by people other than Alexander. By putting Alexander in the statue it makes it clear who his successor should be. It is however disputed whether or not Philip constructed this monument or whether Alexander had it constructed later in which case the motives would be different.
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