The battle of Lemnos of 73 B.C. was a naval victory won by Lucius Licinius Lucullus early in the Third Mithridatic War over a Pontic fleet commanded by the Roman renegade Marcus Varius. The battle was fought in the aftermath of Lucullus's victory at Cyzicus. In the aftermath of his own victory at Chalcedon, Mithridates VI of Pontus had attempted to capture the city of Cyzicus, but Lucullus had imposed a blockade on the Pontic army, and as winter approached Mithridates was forced to abandon the siege. The Pontic army suffered heavy losses during the attempted retreat, and only a fragment of it reached safety at Lampsacus.
Despite the destruction of much of his army, Mithridates still had a powerful fleet, with which he rescued the troops besieged in Lampsacus. Mithridates then split his forces. He took most of them east to Nicomedia, where he hoped to make a stand, but 50 ships and 10,000 picked men were sent west, into the Aegean. This fleet was placed under the command of Marcus Varius, a Roman sent to help Mithridates by Sertorius, the rebel governor of Spain, along with Alexander the Paphlagonian, and Dionysius the eunuch.
By this point Lucullus had raised a fleet from Rome's allies in Asia, after refusing an offer of funds from the Roman senate. He now left part of that fleet to operate in the Propontis while he led the rest of it against Varius.
According to Appian part of the Pontic squadron was destroyed in a storm soon after leaving Lampsacus. Lucullus then captured another thirteen ships at the "harbour of the Achaeans", near Ilium, leaving Varius with less than forty ships. There may have been a first battle near Tenedos, although this may be a mistake for Lucullus's victory in the same location during the First Mithridatic War.
The final clash between Lucullus and the Pontic fleet came at a barren island close to Lemnos. The main Pontic force was ashore on the island when the Romans appeared, and although Lucullus attempted to tempt them out to sea they refused to take that risk.
Lucullus then sent part of his fleet to the far side of the island, where he landed part of his army. These troops forced most of the Pontic force to take to its ships, but they still didn’t dare venture out to sea, and so for some time were caught in a crossfire between the Roman fleet and troops on the island. Eventually, having suffered heavy losses, the survivors fled.
Varius, Alexander and Dionysius were captured in a cave on the island. Dionysius took poison, Varius was killed so that he would not mar Lucullus's triumph and Alexander was taken prisoner. The defeat of Mithridates's main fleet in the Aegean freed Lucullus to invade Pontus, where he would expel Mithridates from his kingdom, before becoming bogged down in a campaign in Armenia.