Dicaearchus of Messana (ˌdɪkeɪˈɑːrkəs...məˈsɑːnə; Δικαίαρχος Dikaiarkhos; 370/350-post 323 BC), also written Dikaiarchos (ˈdɪkaɪɑːrk), was a Greek philosopher, geographer and author. Dicaearchus was a student of Aristotle in the Lyceum. Very little of his work remains extant. He wrote on geography and the history of Greece, of which his most important work was his Life of Greece. Although modern scholars often consider him a pioneer in the field of cartography, this is based on a misinterpretation of a reference in Cicero to Dicaearchus' tabulae, which does not refer to any maps made by Dicaearchus but is a pun on account books and refers to Dicaearchus' Descent into the Sanctuary of Trophonius. He also wrote books on ancient Greek poets, philosophy and politics.
He was the son of one Pheidias, and born at Messana in Sicily, Magna Graecia, though he passed part of his life in Greece, and especially in Athens and the Peloponnesus. He also travelled to make his measurements of mountains. He was a disciple of Aristotle and a friend of Aristoxenus (a letter written to him is attested in Cicero). Eighteenth- and early nineteenth-century scholarship often considered him a friend of Theophrastus as well, but this is based on the reference to a man named Theophrastus in the spurious Description of Greece, which is transmitted under Dicaearchus' name but actually consists of excerpts from a geographic poem written by Dionysius, son of Calliphon, and from a prose periegesis of Greece, written by Heraclides Criticus. It is uncertain when Dicaearchus died. The only certain terminus post quem is the death of Alexander the Great (323 BC). According to Pliny, Dicaearchus measured mountains "with the support of the kings" (cura regum). Most scholars identify these kings as Cassander and Ptolemy I Soter. If this identification is correct, this would put Dicaearchus' activity between 306 and 287 BC. However, the kings might also refer to Philip III Arrhidaeus and Alexander IV, who were the nominatim kings after the death of Alexander the Great.