According to ancient Indian mythology, weapons like the Brahmastra and its variations, the Brahmanda Astra, and the Brahmashirsha Astra were used in the war of Mahabharata and were collectively named Brahma weapons. The weapon called Brahmashirsha Astra was said to have the power of destroying the world. Other than Brahmana-Astra, all of these weapons have been developed by Lord Brahma.
It has been specified as a fiery weapon which could launch a fireball. After the soil samples from the Battlefield of Kurukshetra in the epic story of Mahabharata were analysed, the modern speculations say that it was perhaps a nuclear weapon.
Brahmastra has been used or threatened to be used in Sanskrit mythological scriptures, this includes:
Maharaja Kaushika - Brahmastra has been used by Maharaja Kaushika, later called Brahmarshi Vishvamitra, against Maharishi Vasishta, but it is said that Brahmadanda Astra of Vasishta swallowed the Brahmastra.
Indrajit from Ramayana - Nagasthira was used by Indrajit in his fight against the army of Rama in the Ramayana. The weapon struck Lakshmana and fell. The brothers and their army were saved from death only because of the Sanjeevani herbs brought by Hanuman. The Brahmastra was used by Indrajit against Hanuman as well, but Hanuman was able to survive due to the boon which he had previously received by Lord Brahma.
Shri Rama from Ramayana - Shri Rama used a Brahmastra several times in the Ramayana: once against Jayanta when Sita was hurt by him, once again against Mareecha in their last encounter, and the last time Brahmastra was used in the final battle against the Asura emperor Ravana. The Ramayana says that the weapon has also been aimed at Varuna for the purpose of carving a path through the sea so that the army of Rama could march comfortably towards the island of Lanka. However, as Rama was loading the weapon, Varuna appeared in front of the king and offered its help in crossing the ocean. But the Brahmastra had to be discharged once it was invoked, thus it was instead aimed towards Drumatulya, locating to modern-day Rajasthan, and caused it to become a desert for decades to come.
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Back to Ancient Times:
The old Hindu texts of ancient India have described the battles known as Ancient Hindu wars. There were major wars which took place with the motive to uphold the Dharma over Adharma. It has often been described that these wars took place with the purpose of removing rulers or demonic beings and lords who pursued wars for domination and ambition. According to Hindu teachings, the war was prescribed only as a final option if the peaceful methods did not work or were exhausted. But, when this time appears, war is considered to be a matter of social importance and great person, where every man belonging to the warrior caste must carry out his duty, exemplifying fearsome prowess, courage and honour against all odds and even if it costs his life.
Gods and the weapons:
All the major gods, involving Vishnu, Brahma and Shiva, have often engaged in wars, either in their true form or in the form of Avatars. Astra, celestial weapons with fearsome supernatural power, has been used by them and many other Hindu heroes as an aid for them in battles.