The finds of micro- and macro-subfossils of the walnut (Juglans regia L.) in southeastern Europe strongly suggest that this tree was introduced by man. The appearance of Juglans in Greece is connected with that of Castanea and Platanus. The time of arrival of this species and a way in which it was possibly introduced on the southern mainland of Greece will be discussed in this article with reference to a pollen diagram from Lake Trikhonis. A relation of the walnut with the Mycenaean culture is suggested, linked in time with the Santorini eruption.