The Siege of Rhodes (305 BC/304 BC) was part of the Fourth War of the Diadochi and one of the most notable sieges of antiquity, when Demetrius Poliorcetes, son of Antigonus I, besieged Rhodes in an attempt to break its alliance with Ptolemaic Egypt.

Rhodes was strongly fortified and Demetrius was unable to prevent supply ships from running though his blockade so at first conquering the harbour was his main priority. He first built his own harbour alongside and constructed a mole from which he deployed a floating spiked boom but Demetrius never succeeded in taking the harbour. At the same time his army ravaged the island and built a huge camp next to the city but just out of missile range. Early in the siege the walls were breached and a number of troops entered the city but they were all killed and Demetrius didn't press the attack. The walls were subsequently repaired.

Both sides used many technical devices during the siege such as mines and countermines and various siege engines. Demetrius even built the now notable siege tower, known as the Helepolis, in his attempt to take the city.

The citizens of Rhodes were successful in resisting Demetrius; after one year he abandoned the siege and signed a peace agreement (304 BC) which Demetrius presented as a victory because Rhodes agreed to remain neutral in his war with Ptolemy (Egypt). The unpopularity of the siege may have been a factor in its abandonment after only one year.

Several years later the Helepolis, which had been abandoned, had its metal plating melted down and, along with the money from selling the remains of the siege engines and equipment left behind by Demetrius, was used to erect a statue of their sun god, Helios, now known as the Colossus of Rhodes, to commemorate their heroic resistance.