The Mauryan empire was the first empire that managed to unite all of India. This was partly because of their complex army structure.
Like most ancient Indian armies, the Mauryan army had 4 types of troops- elephant (Gaja), chariot (Ratha), cavalry (Turanga), and infantry (Pada).
Indian armies of this period had within them a basic unit called the Patti, a mixed platoon comprising one elephant carrying three archers or spearman and a mahout, three horse cavalrymen armed with javelins, round buckler, and spear, and five infantry soldiers armed with shield and broadsword or bow. This twelve-man unit, when assembled in three units, formed a Senamukha, or “company.” Three of these formed together comprised a Gulma, or “battalion.” Units were added in multiples of three, forming an Aksauhini, or “army,” comprised of 21,870 Patti. Sources also speak of military units formed around multiples of ten, and there were no doubt units of single arms that could be employed individually or in concert with other arms. The Arthasastra mentions a unit called the Samavyuha, or “battle array,” that was about the size of a Roman legion (5,000 men). This unit comprised five subunits joined together, each subunit containing 45 chariots, 45 elephants, 225 cavalry, and 675 infantrymen each. It goes without saying that managing such units in battle required a high degree of tactical sophistication.
The Mauryan army had multiple Aksauhini's. The standing army had three-quarter million troops, one of the largest armies in the world at the time.
A variety of formations were used in the Mauryan army. Formations were known as vyuha, each one had a centre, two flanks, and two wings. There were thirty main vyuha used, divided into four main categories. One example of a vyuha would be the Padma vyuha or lotus formation.
Padmavyuha is like a lotus trap when enemy's army attacks the lotus bud opens to take them in and once they reach the base the lotus buds close and enemy's army gets trapped between 5 layers of foot soldiers, elephants charioteers and cavalry who are in constant motion.
The Garuda Vyuha or eagle formation was another commonly used formation.
The Garuda Vyuha had a 'beak' where the best elite Kshatriya soldiers would be placed in a tight wedge formation. The 'head,' behind the beak had a small contingent of reserves, also of good quality. Often, war elephants would be placed in the beak and head. Two broad 'wings' would sweep out behind the head, with the swiftest troops- the chariots and cavalry at the outside. Behind the wings, the body would consist of reserves.
Some other formations:
Suchi Vyuha- Needle formation
Chayana Vyuha- Hawk formation
Mala Vyuha- Garland formation
Karuncha vyuha- Heron formation
Makara vyuha- Fish formation
Padma vyuha- Lotus formation
Kurma vyuha- Turtle formation
Trishula vyuha- Trident formation
Chakra vyuha- Wheel or Discus formation
Garuda vyuha- Eagle formation
The Mauryan army was composed of people all over the subcontinent. In addition, Chandragupta Maurya did not discriminate against different castes. As a result, there were soldiers in his army from all castes, making the army very diverse.
The core of the army was composed of Uttarapathian warriors, from central and western India. Uttarapatha had many militaristic peoples – like the Kambojas, Yavanas, Sakas and Vardas. Other peoples in the Mauryan army were the Maghadas, Assamese, and Cheras. Even the Nagas (literally serpents, because they worshiped cobras), a mystical people to the east, were incorporated into the army.