The conquest of Cyprus (306 BC) was an early success for Demetrius Poliorcetes during the Fourth Diadoch War (307-301 BC). The island had been held by Ptolemy I, the ruler of Egypt, for at least a decade before the war, and gave him a naval base that threatened the coast of southern Asia Minor and northern Syria, both areas held by his main opponent Antigonus I (the father of Demetrius).
Demetrius had spent the previous year in Athens, where in 307 he had been heralded as a divine liberator after expelling the forces of Cassander, the ruler of Macedonia. When he left Athens to sail for Cyprus he was accompanied by a fleet of 30 Athenian quadriremes. They would make up part of a multinational fleet that Demetrius would take to Cyprus.
One place that did not contribute to that fleet was Rhodes. That island had remained largely neutral during the Diadochi Wars, and had become increasingly wealthy as a result. They also had a small but powerful fleet. Demetrius’s route east would inevitably take him close to Rhodes, and he issued a demand for help in the upcoming campaign. Not surprisingly neutral Rhodes refused, and Demetrius sailed on. He would return the next year (siege of Rhodes, 305-304 BC).
Demetrius invaded Rhodes with a fleet that probably contained 160 warships, of which 110 were triremes and quadriremes (three or four rows of oarsmen on each side) and 53 heavier ships, the largest being Phoenician heptereis with seven rows of oarsman, and with an army of 15,000 infantry and 400 cavalry. He landed near to Karpasia, in the north east of Cyprus, captured Karpasia and Ourania, and then marched south west towards Salamis, the main Greek city on the island.
Demetrius then began the siege of Salamis, the first of his great sieges. He built a massive siege tower, the Helepolis, the precursor of the more famous tower used at Rhodes, but despite having a huge siege train he was unable to take the city.
Ptolemy responded to the attack on Cyprus in person, at the head of a fleet of 140 warships and an army 10,000 strong. He landed at Paphos, on the west of Cyrpus, then travelled along the south coast to Kition. His plan was to form a junction with Menelaos, after which he would outnumber Demetrius. In order to achieve this he attempted a night dash to Salamis, hoping to catch Demetrius out.
Instead he found Demetrius formed up ready for battle outside the city. The resulting naval battle of Salamis was a crushing defeat for Ptolemy, who was said to have lost 120 of his 140 warships and 8,000 of his 10,000 men. He was forced to retreat back to Egypt, while Menelaos had no choice to surrender. The remaining Ptolemaic possessions on Cyprus soon followed suit. Demetrius took another 8,000 prisons from Salamis and the rest of the island, of whom a significant number were mercenaries willing to change sides after a defeat (unusually many of the men captured during the battle refused to do so).
Cyprus remained an Antigonid for the next ten years, even after the death of Antigonus at Ipsus (301 BC). The victory on Cyprus also gave Antigonus the opportunity to claim the title of king. The last acknowledged legitimate king of Macedonia, Alexander the Great’s son Alexander IV, had been murdered in 310, but in the intervening four years none of the successors had been given a real chance to claim the title. Cyprus gave Antigonus the military victory he needed to give his adoption of the royal title some credibility. Once he had been acclaimed as king, Antigonus bestowed the same title on Demetrius.