Leosthenes (in Greek Λεωσθένης; died 323 BC) was an Athenian, commander of the combined Greek army in the Lamian war. We know not by what means he had obtained the high reputation which we find him enjoying when he first makes his appearance in history: it has been generally inferred, from a passage in Strabo, that he had first served under Alexander the Great in Asia; but it now seems certain that this is a mistake, and that Leonnatus is the person there meant.
It is certain that when we first meet with any distinct mention of Leosthenes, he appears as an officer of acknowledged ability and established reputation in war, but a vehement opponent of the Macedonian interest. Shortly before the death of Alexander he had collected together and brought over to cape Taenarum a large body of the Greek mercenaries that had been disbanded by the different satraps in Asia, according to Alexander's orders. As soon as the news of the king's death reached Athens, Leosthenes was despatched to Taenarus to engage the services of these troops, eight thousand in number: from thence he hastened to Aetolia, and induced that people to join in the war against Macedonia. Their example was followed by the Locrians, Phocians, Dorians, and many of the Thessalians, as well as by several of the states of the Peloponnese; and Leosthenes, who was by common consent appointed commander-in-chief, assembled these combined forces in the neighbourhood of Thermopylae. The Boeotians, who, through fear of the restoration of Thebes, adhered to the Macedonian interest, collected a force to prevent the Athenian contingent from joining the allied army; but Leosthenes hastened with a part of his forces to assist the Athenians, and totally defeated the Boeotian army. Antipater now advanced from the north, but with a force very inferior to that of the confederates: he was defeated in the first action near Thermopylae, and compelled to throw himself into the small town of Lamia. Leosthenes, desirous to finish the war at a blow, pressed the siege with the utmost vigour; but his assaults, were repulsed, and he was compelled to resort to the slower method of a blockade. While he was engaged in forming the lines of circumvallation, the besieged made a vigorous sally, in which Leosthenes himself received a blow on the head from a stone, of which he died three days after. His death was felt as a great discouragement to the cause of the allied Greeks; and Pausanias is probably right in regarding it as the main cause of their ultimate failure. Phocion's remark, on the other hand, is well known, that "he was very well fitted for a short course, but not equal to a long one." It is certain that Leosthenes gave proofs of no common energy and ability during the short period of his command; and his loss was mourned by the Athenians as a public calamity. He was honoured with a public burial in the Ceramicus, and his funeral oration was pronounced by Hyperides. His death took place before the close of the year 323 BC: though still quite a young man, it appears that he left children, whose statues were set up by the side of his own in the Piraeus.