|Centuries:||1st century – 2nd century – 3rd century|
|Decades:||140s 150s 160s – 170s – 180s 190s 200s|
|Years:||168 169 170 – 171 – 172 173 174|
|171 by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishment and disestablishment categories|
|Establishments – Disestablishments|
|Ab urbe condita||924|
|Bahá'í calendar||−1673 – −1672|
|English Regnal year||N/A|
|Chinese calendar||庚戌年 (Metal Dog)
2867 or 2807
— to —
辛亥年 (Metal Pig)
2868 or 2808
|Coptic calendar||−113 – −112|
|- Vikram Samvat||227–228|
|- Shaka Samvat||93–94|
|- Kali Yuga||3272–3273|
|Igbo calendar||−829 – −828|
|Iranian calendar||451 BP – 450 BP|
|Islamic calendar||465 BH – 464 BH|
|Minguo calendar||1741 before ROC
|Thai solar calendar||714|
|Wikimedia Commons has media related to 171.|
Year 171 (CLXXI) was a common year starting on Monday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Severus and Herennianus (or, less frequently, year 924 Ab urbe condita). The denomination 171 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
- Emperor Marcus Aurelius forms a new military command, the praetentura Italiae et Alpium. Aquileia is relieved, and the Marcomanni are evicted from Roman territory.
- Marcus Aurelius signs a peace treaty with the Quadi and the Sarmatian Iazyges. The Germanic tribes of the Hasdingi (Vandals) and the Lacringi become Roman allies.
- Armenia and Mesopotamia becomes a protectorate of the Roman Empire.
- The Costoboci cross the Danube (Dacia) and ravage Thrace in the Balkan Peninsula. They reached Eleusis, near Athens, and destroyed the temple of the Eleusinian Mysteries.
- In May or June, the orator Aelius Aristides delivered a public speech in Smyrna, lamenting the damage recently inflicted to the sacred site of Eleusis.