Ptolemy sailed up with a great fleet and tried to bring the Greek cities to revolt, while Lysimachus invaded upper Macedonia from Thrace and ravaged the country. So Pyrrhus, taking the field at the same time with these, marched against Beroea, expecting, as proved to be the case, that Demetrius would go to confront Lysimachus, and thus leave the lower country unprotected.
Edition :
Plutarch Lives IX: Demetrius and Antony, Pyrrhus and Caius Marius, Ed. Jeffrey Henderson, trans. Bernadotte Perrin (The Loeb Classical Library 101), Harvard University Press: Cambridge/MA - London 1968 (first ed. 1920).
Remark :
date: The date is taken from the New Pauly.
http://referenceworks.brillonline.com/entries/brill-s-new-pauly/lysimachus-e714860 titel: Pyrrhus conquers the country after Demetrius left it unprotected to fight Lysimachus. This is mentioned in 11.2-6.
