The term Hellenistic (derived from Héllēn, the Greeks' traditional self-described ethnic name) was established by the German historian Johann Gustav Droysen to refer to the spreading of Greek culture and colonization over the non-Greek lands that were conquered by Alexander the Great in the 4th century BC. The Hellenistic age marks the unification of the Greek world, sharing a common culture based on that of 5th and 4th century BC Athens, along with a fusion of Near Eastern cultures. Roy M. MacLeod, The Library Of Alexandria: Centre Of Learning In The Ancient World The period is characterized by a new wave of Greek colonization which established Greek cities and Kingdoms in Asia and Africa. Ulrich Wilcken, Griechische Geschichte im Rahmen der Alterumsgeschichte. Those new cities were composed by Greek colonists who came from different parts of the Greek world, and not from a specific "mother city" (metropolis) as before. The main cultural centers expanded from mainland Greece, to Pergamon, Rhodes, as well as to new Greek colonies such as Antioch and Alexandria. This mixture of Greek-speakers gave birth to a common Attic-based dialect, known as Hellenistic Greek, which came to absorb and replace all idioms of the Greek language.