In southern Macedonia Perseus had fortified the north bank of the Elpeus River to prevent Paullus from entering his kingdom from the south. Paullus therefore designed a circling movement around Mount Olympus to flank Perseus. He appointed Corculum to head this operation, assisted by Quintus Fabius Maximus Aemilianus (Paullus' natural son, adopted into the Fabii); Corculum said he and Fabius volunteered. According to Polybius, Corculum took 5,000 men with him (Corculum said 8,320 men in his memoir). At first, he faked a movement to the sea, but once at Heracleum he told his staff the real purpose of the mission, and moved by night to Pythium (departing in the night of 17 and 18 June 168). Meanwhile, Paullus attacked the Macedonians to prevent them from detecting Corculum's move. Pythium was successfully taken in the early morning of 20 June 168, perhaps because the garrison was still asleep. Corculum's version is different, as he wrote that a deserter warned Perseus of the flanking manoeuvre; he therefore had to face a force of 12,000 men, whom he defeated—and also personally killed a giant Thracian. Livy, following Polybius, tells the Macedonians were only 5,000, a number favoured by modern historians. In any case, after hearing of the capture of Pythium, Perseus retreated north, and set his camp just before Pydna. Corculum then completed the turning movement around Mount Olympus and met with Paullus (who had followed Perseus) on 21 June. Livy says that Corculum and other officers in Paullus' staff wanted to attack Perseus immediately, but the consul preferred to delay in order to rest the troops.