Chakra Vyuha is considered to be the most complex war formation in Mahabharata. From the Pandava side, it was known only to Lord Krishna, Arjuna, Pradyumna and Abhimanyu. From the Kourava side, it was known only to Drona. On the 13th day Kurukshetra war, the Kourava troops were arranged in this formation by Drona who was the Kourava commander during that time. Abhimanyu successfully penetrated inside Chakra Vyuha and caused a vast carnage in the Kourava army. He died on the same day, after he was unable to counter a combined group attack by Drona, Karna, Kripa, Ashwatthama and Kritavarma.
Chakra Vyuha is a multi-level defensive formation of soilders which constantly rotates in the shape of a spinning discus as implied by the word ‘Chakra.’ The formation looks like concentric circles arranged parallelly in layers. The formation starts with a large number of soilders stationed at the centre. The soilders continue to move spirally till the completion of seven concentric layers. Each concentric layer rotates in alternate directions at different velocities thus perplexing an enemy warrior who tries to enter inside the formation.
The core of Chakra Vyuha which looks like a large dot comprises of the foremost warriors of the army. In Drona’s Chakra Vyuha, it consisted of Karna, Kripa, Ashwatthama and Kritavarma apart from him. The soilders of four classes, namely infantry, cavalry, elephant riders and chariot fighters are arranged at different levels of the seven concentric layers. Each of the seven layers has an interleaving position which is protected by a group of powerful warriors to make the layers strongholds of defence. Some able warriors of the army are strategically arranged in openings maintained at different levels of a concentric layer. In addition to that, there are two sets of interlocked positions to make Chakra Vyuha an impregnable military formation. Finally the last of the concentric layers merges inside the body of Chakra Vyuha. The last concentric layer serves as the line of demarcation which separates the two sets of interlocked positions.
The area where the last concentric layer merges with the body of the formation is the entrance to penetrate inside the formation. In Drona’s Chakra Vyuha, it was protected by Jayadratha. Owing to a boon of Lord Shiva, the Pandava warriors were checked by Jayadratha from penetrating inside Chakra Vyuha. Therefore they could not proceed furthur to help Abhimanyu, who had already penetrated the Vyuha much earlier. Furthurmore the constant rotating concentric circles of the Kourava soilders at alternate directions puzzled the Pandava warriors and halted their progress.
Speaking of Abhimanyu, he successfully penetrated inside Chakra Vyuha as he learnt the art of penetrating this formation from his father Arjuna. Abhimanyu caused a vast carnage in the Kourava army at different levels of Chakra Vyuha. He was finally brought down by a combined attack of Drona, Karna, Kripa, Ashwatthama and Kritavarma in the centre of the Vyuha. Worn out with exhaustion, he was ultimately killed by Dusshasana’s son in a mace fight.
Till date, Abhimanyu’s death remains the only instance where a warrior was brought down by a combined attack of enemy warriors.