Year 168 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Macedonicus and Crassus (or, less frequently, year 586 Ab urbe condita). The denomination 168 BC for this year has been used since the early medieval period, when the Anno Dominicalendar era became the prevalent method in Europe for naming years.
The king of Illyria, Gentius, is defeated at Scodra by a Roman force under Lucius Anicius Gallus and then brought to Rome as a captive to be interned in Iguvium. This loss removes Illyria as an important ally for Macedonia and effectively weakens Perseus of Macedon in his battle with Rome.
June 22 – The Battle of Pydna (in southern Macedonia) gives Roman forces under Lucius Aemilius Paulus a crushing victory over Perseus and his Macedonian forces, thus ending the Third Macedonian War. Perseus is captured by the Romans and will spend the rest of his life in captivity at Alba Fucens, near Rome.
The Macedonian kingdom is broken up by the Romans into four smaller states, and all the Greek cities which have offered aid to Macedonia, even just in words, are punished. The Romans take hundreds of prisoners from the leading families of Macedonia, including the historian Polybius.
Antiochus IV then invades Egypt again and occupies Lower Egypt and his forces camp outside Alexandria. However, the Roman ambassador in Alexandria, Gaius Popillius Laenas, intervenes. He presents Antiochus IV with an ultimatum that he evacuate Egypt and Cyprus immediately. Antiochus, taken by surprise, asks for time to consider. Popillius, however, draws a circle in the earth (i.e. "a line in the sand") around the king with his walking stick and demands an unequivocal answer before Antiochus leaves the circle. Fearing the consequences of a war with Rome, the king agrees to comply with the ambassador's demands. In return, the Romans agree that Antiochus IV can retain southern Syria, to which Egypt has laid claim, thus enabling Antiochus IV to preserve the territorial integrity of his realm.