The problem of the evolution of the kouros type is inevitably linked to that of the overall development of monumental Archaic Greek sculpture. There are fundamentally two schools of thought on how those Daedalic forms, some of which we know of only from the literature (kolossos, bretas, andrias and xoanon), became the free-standing sculpture in around the 6th century; namely, that it was a response to the internal development of Greek types and religious needs or a product of foreign influence. For an external cause for change, possible sources of influence have been cited, such as Egypt, Anatolia and Syria, with the strongest case made for Egypt. It is known that the Greeks had longstanding trade relations with Egypt prior to the founding of the Greek entrepôt of Naukratis in the mid-7th century, where the Greeks could have learned Egyptian sculpting methods.