A "katoikia" () was similar to a "polis", typically a military colony, with some municipal institutions, but not those of a full "polis." The word derives from the for "to inhabit" (a settlement) and is somewhat similar to the Latin "civitas". In the Classical era, there were few "katoikiai"; however, with the rise of large centralized empires following the conquests of Alexander the Great, they became the main type of Greek settlement, especially in the newly conquered east. Sometimes these were fortresses, inside a city or in an open position. They were an equivalent of the English idea of a fort.