171 BC

By place

Greece

• Epirus joins Macedonia in the latter's fight against Rome. However, the leagues of southern Greece remain neutral.
• Thanks to the efforts of Eumenes II of Pergamum while in Rome, the Romans declare war on Macedonia and send troops to Thessaly, thus beginning the Third Macedonian War. In the resulting Battle of Callicinus the Macedonians, led by their king, Perseus, are victorious over a Roman force led by consul Publius Licinius Crassus.
• Boiotian League dissolved by the Romans.

  Roman Republic

• The first Roman colony outside Italy is founded at Carteia in southern Hispania after Iberian-born descendants of Roman soldiers appear before the Roman Senate to request a town to live in and are given Carteia, which is named Colonia Libertinorum Carteia.
• Lucius Postumius Albinus is sent by Rome as an ambassador to King Masinissa of Numidia, and to the Carthaginians in order to raise troops for the war against Perseus of Macedonia.

  Parthia

• Mithradates I succeeds his brother Phraates I as king of Parthia.