The Diadochi (literally, ‘successors’) were the military commanders and administrators who vied for supremacy over the cities and regions conquered by Alexander III ‘the Great’ of Macedon after his death in 323 BCE. By 300 BCE the empire had fragmented into four principal regions administered (from west to east) by Cassander, Lysimachus and Seleucus, and by Ptolemy in Egypt to the south. Over the ensuing century, further fragmentation was to occur under the ‘Epigoni’, their descendants. In 297 BCE, following the death of Cassander, Demetrius, son of Antigonus, seized the throne of Macedon and embarked on military expansion. He harried Lysimachus in Thrace, engaged Ptolemy in the eastern Mediterranean, and with massive siege engines took Athens, but in 285 BCE he was captured by Seleucus and died soon afterwards, being succeeded by his son Gonatas. Seleucus, meanwhile, was ceding territory in the east to local encroaching non-Greek chieftains, and the independent Greek kingdom of Bactria was emerging. Various city states on the Greek mainland formed the second Achaean League as a federal alliance against the Macedonians and to preserve the Hellenistic culture throughout the remaining empire. Under Aratus of Sicyon the League mounted a powerful challenge to both the Macedonians and the rival Aetolian League, centred on Sparta. Supported by Ptolemy III, between 243 and 229 BCE, Aratus captured Corinth, Megalopolis, and Argos, and made peace with Gonatas. In 220 BCE war broke out between the two Leagues, and in 200 BCE the Achaeans allied with the expanding Romans against the Macedonians. This marked the beginning of the Roman takeover of the Greek world.