At the start of the Third Mithridatic War the Roman consul Marcus Aurelius Cotta took the his fleet into the Bosphorus; he made his headquarters at Chalcedon, a major port city in Bithynia. Mithridates marched his army into Bithynia while his fleet sailed to the Bosphorus. Most of Bithynia, outraged by Roman exploitation, welcomed Mithridates and he was able to advance very rapidly. Cotta decided to make his stand at Chalcedon with the Roman/Allied fleet at his back. He also sent urgent messages to Lucius Licinius Lucullus, his consular partner who was preparing his army in Asia province, that the Pontic invasion was underway and he needed assistance.
The Battles
Nudus, Cotta's naval prefect, convinced the consul to let him take the field against Mithridates. He took up a fortified position outside the city and waited for the Pontic army to make the first move.
Mithridates sent his forces, led by Bastarnaemercenaries, against the Roman positions outside Chalcedon. Nundus and his men were overwhelmed by the speed and professionalism of the numerically superior Pontic army. The Romans and their allies fell back on the city, but got caught trying to get through the gates. First Pontic archers and slingers fired at the tight-packed Romans trying to get into the city, then the Pontic infantry charged. The city defenders had no choice but to drop the portcullis to prevent Mithridates' men from getting inside. This left a large portion of the Roman forces outside the walls. Nundus and some of his officers were pulled over the ramparts by rope but most men were slaughtered; some 3,000 Roman-Allied soldiers were killed before Chalcedon's walls.
Mithridates followed up his success with a combined land and sea assault on the harbour. An advance party of Bastarnae managed to break the bronze chain which blocked entrance to the port and the Pontic fleet sailed in. Four ships were sunk and sixty ships, the rest of Cotta's fleet, were captured and towed away. The city itself remained in Roman hands, but there was little that Cotta could do.
Losses
The Romans lost 4,000–5,300 on land, 3,000–8,000 perished during the battle for the harbour and 4,500 were captured. Mithridates lost only 30 Bastarnae and 700 others dead.
Aftermath
With Cotta bereft of an army and fleet, his local support melted away, Nicaea, Lampsacus, Nicomedia and Apameia, all major cities in the region, fell to Mithridates or opened their gates to him. Only nearby Cyzicus held to the Roman cause, probably because many of its citizens had died fighting against Mithridates at Chalcedon. The Pontic army marched on Cyzicus and began a siege, hoping to take the city before Lucullus could arrive. During the siege of Cyzicus Lucullus was able to established a counter-siege; Mithridates' army was destroyed by famine and plague and the king fled back to Pontus. But the war was far from over and would rage on for another decade.
