Antigonus then sent his son Demetrius to regain control of Greece. In 307 he took Athens, expelling Demetrius of Phaleron, Cassander's governor, and proclaiming the city free again. Demetrius now turned his attention to Ptolemy, defeating his fleet at the Battle of Salamis and taking control of Cyprus. In the aftermath of this victory, Antigonus took the title of king (basileus) and bestowed it on his son Demetrius Poliorcetes, the rest of the Diadochi soon followed suit. Demetrius continued his campaigns by laying siege to Rhodes and conquering most of Greece in 302, creating a league against Cassander's Macedon.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): When did Demetrius take control of Athens?
307