Year 161 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Messalla and Strabo (or, less frequently, year 593 Ab urbe condita). The denomination 161 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 rebel Seleucid general and ruler of Media, Timarchus, who has distinguished himself by defending Media against the emergent Parthians, treats Demetrius I's violent accession to the Seleucid throne as the excuse to declare himself an independent king and extend his realm from Media into Babylonia.
With the restoration of peace in Judea, an internal struggle breaks out between the supporters of Judas Maccabeus and the Hellenist party. The influence of the Hellenic Party all but collapses in the wake of the Seleucid defeat.
The Jewish High Priest Menelaus, who is supported by the Hellenist party, is removed from office and is executed. His successor is a moderate member of the Hellenist party, Alcimus. However, when Alcimus executes sixty Jews who are opposed to him, he finds himself in open conflict with the Maccabees. Alcimus flees from Jerusalem and goes to Damascus to ask the Seleucid king, Demetrius I, for help.
The Maccabees, led by Judas Maccabeus, and a Seleucid army, led by the Seleucid general Nicanor, fight the Battle of Adasa, near Beth-horon. Maccabeus wins the battle and Nicanor is killed.