The typical Hellenistic army relied on long spears a shield wall to form a phalanx and defeat their enemy head on. The Greeks also relied primarily on well trained and equipped heavy infantry but their strategies were as a whole less advanced than the Roman's and when Mithridates, the last Hellenistic king to challenge Rome, fought his last war he switched from the Greek phalanx formations to imitation Roman armies trained by Roman exiles and mercenaries. However, many of Rome's early enemies fielded armies of this sort and they had a significant influence on the formation of both the Roman legions and Parthia as Alexander the Great used phalanxes to conquer Persia and his successor state, the Seleucid Empire continued to use them until it was defeated and divided by Rome and Parthia. They had advanced siege techniques and engineering and influenced the Romans heavily in these fields.