The Eight Legions (Sanskrit: अष्टसेना, Aṣṭasenā; 八部衆) are a group of Buddhist deities whose function is to protect the Dharma.
For that size of a military unit there is a fitting Sanskrit term "Dhvajinī", i.e. "body of troops bearing a standard".
"Sena" is better to translate as "army" due to the fact that enormous Kuru and Pāṇḍava troops that gathered on the battlefield were called "kurupāṇḍava-sena" (one can't label two huge military forces fighting each other as just one legion), and more than that, all wars in India are patronized by the god of war Kārtikeya who probably plays both sides in any conflict if adversary combatants worship devas.
There were plenty of legions in India serving various kings and lords, but all military forces as a whole could be figuratively named an army, i.e. "Sena" - the Shakti through which the god of war imposed his will.
While the list of figures within this category vary, the most common are as follows: At Kōfuku-ji in Nara, Japan, there is a famous group of statues that represent the Eight Legions.