While Antigonus was distracted elsewhere, Ptolemy had been expanding his power into the Aegean Sea and to Cyprus. Antigonus thus resumed the war with Ptolemy in 308 BC, beginning the Fourth War of the Diadochi. Antigonus sent his son Demetrius to regain control of Greece, and in 307 BC he took Athens, expelling Demetrius of Phaleron, Cassander's governor, and proclaiming the city free again. Demetrius then turned his attention to Ptolemy, invading Cyprus and defeating Ptolemy's fleet at the Battle of Salamis-in-Cyprus. In the aftermath of this victory, Antigonus and Demetrius both assumed the crown of Macedon, in which they were shortly followed by Ptolemy, Seleucus, Lysimachus, and eventually Cassander.