The Third Syrian War was fought between Ptolemy III and Seleucus II from 246 to 241 B.C. Ptolemy caught the Seleucid Empire in a time of weakness and was able to conquer Syria and much of southern Asia Minor despite being defeated by Antigonus, still an ally of the Seleucids, in 245 B.C. in the naval Battle of Andros.
Sources
Encyclopedia of Military History, Dupuy & Dupuy, 1979