The clustering of large numbers of people into cities, though there is no clear-cut line between large towns and cities, both being characterized by very high population densities. In southeast Europe, urbanization seems to have begun by 4000 BC, in Greece leading eventually to growth of Mycenaean civilization, in Italy (early 1st millennium BC) to Etruscan civilization, etc. Many civilizations, e.g. the Maya, with large ceremonial centers, have wrongly been called "urban.