Mithridates VI of Pontus had already fought Rome once and lost. In the First Mithridatic War (89–85 BC), the Roman general Lucius Cornelius Sulla defeated him and imposed a punishing peace. Mithridates spent the following years rebuilding his army and biding his time. The occasion to move came in 74 BC, when Nicomedes IV, king of Bithynia — the buffer state between Pontus and Rome — died. The Romans claimed he had bequeathed his kingdom to Rome. Mithridates disputed this and marched west.

The Roman governor of Bithynia, Marcus Aurelius Cotta, was not prepared for the invasion. He retreated to Chalcedon, where he had the fleet at his back, and sent urgent word to his former consular colleague Lucius Licinius Lucullus, who had been tasked with the Roman command against Mithridates. Cotta's situation rapidly worsened: he was drawn into battle before Chalcedon's walls, lost 3,000 men, and watched Mithridates seize most of his fleet in a combined land-sea assault. Mithridates left Cotta under siege and turned his main army westward, taking city after city until he reached Cyzicus.

Cyzicus occupied a peculiar position. The city sat on the Kapıdağ Peninsula, connected to the Anatolian mainland by a narrow tombolo — the ancient description of it as a spearpoint aimed inland captures the shape well. To besiege the city effectively, Mithridates had to ship a portion of his army around the peninsula by sea, since the tombolo alone was not wide enough to surround the city completely. He seized the harbor, erected siegeworks, and set his engineers to work.

Pontic engineers under Niconides of Thessaly, Mithridates' chief engineer, assembled a siege tower 150 feet high, along with battering rams, catapults, and large crossbows. These were the tools of systematic reduction — the instruments of a siege intended to break down walls over time. What the engineers and their king could not engineer was a reliable food supply. Cyzicus held out.

When Lucullus arrived and assessed the situation, he made a calculation that his officers found counterintuitive: he would not attack the Mithridatic army. He set up camp on a hill overlooking the city and the siege lines, and he ordered his men to cut Mithridates' supply routes. They succeeded, severing the Pontic army's lines while keeping Roman supply lines open. From his hilltop position, Lucullus was a constant, menacing presence — close enough to threaten, unwilling to give battle.

Mithridates attempted a deception: he sent word to the defenders of Cyzicus that the Roman army on the hill was actually his own reserve. Lucullus countered by sending one of his men through the siege lines. That man had to swim seven miles to reach the city — doing so, the source notes, with the aid of a flotation device — and convince the Cyzicans that the army watching from the hill was their ally, not their enemy. They held on.

With winter arriving, the Mithridatic army's situation became desperate. Starvation spread through the camp. Plague followed, brought on — the sources report soberly — by corpses left unburied among the soldiers. The men who had marched to Cyzicus in overwhelming numbers were dying not in battle but of hunger and disease, cold and exposure. The king who had rebuilt his power after defeat by Sulla now faced something worse than military reversal: the slow disintegration of an army from within.

When Mithridates finally decided to withdraw, he used the cover of winter weather to break through Lucullus's encirclement and march his surviving forces toward Lampsacus on the Hellespont. But the army that reached Lampsacus was not the one that had set out. On the road, Lucullus's forces caught up with the retreating column at the Granicus River — the same river where Alexander the Great had won his first victory over Persia in 334 BC — and attacked. The destruction was severe.

Of the approximately 300,000 soldiers who had marched into Bithynia, only around 20,000 effective troops remained by the time Mithridates reached safety. The ancient sources describe the siege as an unmitigated disaster for Pontus. It was not a loss on a battlefield — there was no climactic engagement. It was attrition: the slow arithmetic of a large army consuming more than it could replenish, in hostile terrain, under an opponent who understood that arithmetic better than the king did.

The people of Cyzicus who held the city through the siege of 73 BC were defending something that mattered. The city was, by that point, the leading city of northern Mysia and a Roman ally of long standing. Its gold coins — the cyziceni — had been a standard currency across the Greek world for centuries. Its Temple of Hadrian, not yet built, would eventually rise to a scale that made ancient writers rank it among the wonders of the world. The city that withstood Mithridates was rewarded by Rome with an extension of territory and recognition of its municipal independence.

The men and women inside Cyzicus's walls in the winter of 73–72 BC endured not only the threat of siege weapons but the knowledge that an enormous army encircled them. They watched from their walls as that army starved. The besiegers suffered; the besieged held on. It was, in the end, the city's geography and the patience of Lucullus that decided matters — not heroic assault, but the grinding mathematics of supply.