Year 178 (CLXXVIII) was a common year starting on Wednesday of the Julian calendar. At the time, it was known as the Year of the Consulship of Scipio and Rufus (or, less frequently, year 931 Ab urbe condita). The denomination 178 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.

• Bruttia Crispina marries Commodus, and receives the title of Augusta.^[1]
• Emperor Marcus Aurelius and his son Commodus arrive at Carnuntum in Pannonia, and travel to the Danube to fight against the Marcomanni.

• Last (7th) year of Xiping era and start of Guanghe era of the Chinese Han dynasty.
• In India, the decline of the Kushan Empire begins. The Sassanides take over Central Asia. ^{[citation needed]}

• The Montanist heresy is condemned for the first time.

• Lü Meng, Chinese general (d. 220)
• Peng Yang, Chinese official (d. 214)
• Zhang Cheng, Chinese general (d. 244)

• February 12 – Agrippinus, patriarch of Alexandria
• Song, Chinese empress of the Han dynasty