The battle of Chalcedon was a combined land and sea battle at the start of the Third Mithridatic War that ended in a crushing victory for Mithridates VI of Pontus. During 74 B.C. Mithridates and the Romans had both prepared for war – Mithridates by building a new fleet and a large army, the Romans by sending out the consuls Marcus Aurelius Cotta and Lucius Licinius Lucullus with one extra legion to support the four already in the area. Cotta was given the province of Bithynia, and command of the allied fleet, while Lucullus got Cilicia and command in the upcoming war.
Mithridates made the first move. While Lucullus prepared to invade Pontus from Galatia, he moved west through Paphlagonia and invaded Bithynia. Appian gives Mithridates 140,000 infantry and 16,000 cavalry, gathered from his empire and his allies. Cotta had command of a fleet of 64 ships, most gathered from Rome's allies in the area, and an unknown number of troops.
As Mithridates advanced through Bithynia, Cotta retreated to Chalcedon, just opposite Byzantium on the Asian shore of the Propontis, close to the entrance to the Bosporus. Part of his army, under the command of his naval prefect Nudus took up a position on the plains outside the city to await attack.
The Pontic army, probably under the command of the generals Taxiles and Hermocrates, with Mithridates in attendance, attacked Nudus and forced him out of his position. The Romans were forced to retreat towards the city along a route blocked by 'many walls' (Appian), presumably an area of small fields outside the city. As the refugees attempted to fight their way into the city they suffered heavy casualties Pontic casualties, especially after the gates were shut to prevent the city falling. Nudus and his officers were trapped outside the city, but were pulled up onto the walls by ropes.
Mithridates followed up his victory on land by attacking Chalcedon's harbour, breaking through the chain that blocked the entrance. Four Roman ships were burned and sixty towed away. Appian gives the Roman casualties as 3,000, amongst them the senator Lucius Manlius.
After this defeat Mithridates moved west around the Asia shore of the Propontis to besiege the island city of Cyzicus, then one of the most important ports on the Asian side, leaving Cotta blockaded in Chalcedon. He was unable to follow up on this initial victory. Lucullus abandoned his planned invasion of Pontus, and blockaded Mithridates's army outside Cyzicus. Eventually Mithridates was forced to abandon the siege, suffering very heavy casualties during the retreat.