(Λάμαχος), son of Xenophanes, in the 8th year of the Peloponnesian war, B. C. 424, with a detachment of 10 ships from the tribute-collecting squadron, sailed into the Euxine; and coming to harbour at the mouth of the Calex, near Heracleia, had his ships destroyed by a sudden flood. He succeeded in making his way by land to Chalcedon. (Thuc. 4.75.) His name recurs in the signatures to the treaties of B. C. 421. And in the 17th year B. C. 415 he appears as colleague of Alcibiades and Nicias, in the great Sicilian expedition. In the consultation held at Egesta on their first arrival, in which Nicias proposed a return to Athens and Alcibiades negotiation, Lamachus, while preferring of these two plans the latter, urged, as his own judgment, an immediate attack on Syracuse, and the occupation of Megara, as the base for future attempts, advice which in him may have been prompted less by counsel than courage, but which undoubtedly was the wisest, and would almost certainly have been attended with complete success. In the following year, soon after the investment was commenced, he fell in a sally of the besieged, in advancing against which he had entangled himself amongst some dykes, and got parted from his troops. The loss of his activity and vigour must have been severely felt: his death was one of those many contingencies, each one of which may be thought to have singly turned the scale in the Syracusan contest. (Thuc. 6.8, 49, 101.)

Lanmachus appears amongst the dramatis personae of Aristophanes (Aristoph. Ach. 565, &100.960, 1070, &c.) as the brave and somewhat blustering soldier, delighting in the war, and thankful, moreover, for its pay. Plutarch, in like manner, describes him as brave and honest, and a hero in the field; but so poor, and so ill-provided, that on every fresh appointment he used to beg for money from the government to buy clothing and shoes; and this dependent position he thinks made him backward to take a part of his own, and deferential to his colleagues--Nicias, perhaps, in especial. (Plut. Nic. 16, cf. ib. 12, 13, and Alcib. 18, 20, 21.) Plato also speaks of his valour. (Lach. p. 198.)

If we may trust a passage of Plutarch (Pericles, 20), Lamachus, in an expedition made by Pericles into the Euxine, was left there in charge of 13 ships, to assist the people of Sinope against their tyrant, Timesilaus; after the expulsion of whom the town received 600 Athenian colonists. The precise date of this occurrence can hardly be established : in Plutarch's narrative, it is previous to the Thirty Years' Peace of B. C. 445. He must therefore have been an old man at the time of his last command.