While there are countless weapons mentioned in Hindu mythology and the Mahabharata, two (better said three) specific weapons caught my attention mostly because of their ancient descriptions, and what they seem to resemble to, in modern times.
Belonging to the group of the so-called Brahma weapons are the Brahmastra, and its variants the Brahmashirsha Astra and the Brahmanda Astra. All of these weapons are mention in ancient Sanskrit writings, and all of them were considered supernatural weapons.
One of them—the Brahmashirsha astra—perhaps the second most powerful of them all, was described as a weapon that could destroy the world. In Mahabharata, it is explained that when the Brahmashirsha astra is invoked, “It blazes up with terrible flames within a huge sphere of fire. Numerous peals of thunder were heard, thousands of meteors fell and all living creatures became terrified with great dread. The entire sky seemed to be filled with noise and assumed a terrible aspect with flames of fire. The whole earth with her mountains and waters and trees trembled.” When it strikes an area it will cause complete destruction and nothing will ever grow, not even a blade of grass for the next 12 years. It will not rain for 12 years in that area and everything including metal and earth becomes poisoned.
The Brahmastra, in turn, was a weapon that according to ancient Sanskrit writing, was capable of destroying the entire universe.
Depending on which ancient writing you look at, the Mahabharata, Ramayana and the Puranas, the three weapons are commonly called Brahmastra.
In the Purana, for example, the Bramhastra is considered one of the most powerful supernatural weapons to have ever existed.
Descriptions of the Brahmastra suggest that this mighty weapon never missed its mark, and had to be used with a very specific intent against an army, as its target would be completely destroyed.
Furthermore, Sanskrit writings suggest that the Brahmastra is invoked by a key phrase or invocation, that is given to its user when the weapon is given to him. This is something I find very interesting as it sort of reminds me of Nuclear weapons and nuclear lunch codes belonging to countries. You can’t have one without the other.
The target, when hit by a Brahmastra, would be completely annihilated.
The Brahmashirsha Astra—Brahma’s head missile—was often described as the fifth head of Brahma. This is a weapon that is said to manifests with the fifth head of Brahma at its tip.
According to the Mahabharata, Arjuna and Ashwatthama used the Astra against each other at the end of the Kurukshetra war.
We find the description of the weapons power in the book Ānanda Bhāratī: Dr. K. Krishnamoorthy Felicitation Volume, where we read that the Brahmastra is considered a fiery weapon, that once used, created a massive fireball that threatened the entire world with destruction.
Furthermore, after the weapon was used, the Earth would see decreased rainfall and the soil would develop cracks, like what happens with a drought.
In numerous epics and Vedas, the Brahamastra is considered a weapon of last resort, that must be avoided at all costs in combat.
The best description of the power of this weapon can be found in the Mahabharata where the Brahmastra is defined as a weapon which is said to be a single projective, that contains the power of the universe. It was a mighty weapon. A Powerful Weapon. A weapon of last resort. A weapon that could bring complete annihilation to the world.
“It blazes up with terrible flames within a huge sphere of fire. Numerous peals of thunder were heard, thousands of meteors fell and all living creatures became terrified with great dread. The entire sky seemed to be filled with noise and assumed a terrible aspect with flames of fire. The whole earth with her mountains and waters and trees trembled.”
The Brahmastra was used to destroy inferior divine weapons or counter them. It was described as being as heavy as a mountain but could travel as fast as the wind nevertheless. The Brahmastra was painful as poison and as energetic as fire.