Brahmastra was a deadly arrow obtained after propitiating Brahma Dev. There was no defense against Brahmastra. The person who had
discharged the arrow can call it back. It could only be stopped by Brahmadanda –
a stick created by Brahma.
Brahmastra never misses it mark and it can only be used once
in a day.
It is invoked by a mantra that is bestowed upon the user
when Brahma blesses him with the arrow. The mantra is used to call upon the
weapon when required.
The weapon can be used against an individual or against an
entire army.
The arrow causes severe environmental damage. The land
becomes barren and living beings cannot survive in such a land. There will be
no rainfall. Those residing in the area become infertile.
Brahmastra was used in the Ramayana. Bhagavan Ram used it to
annihilate Ravana.
Another famous usage of Brahmastra was when it was used by
Arjuna and Ashwathama against each other. Arjuna called his weapon back. But
Ashwathama directed it against the unborn grandchild of Arjuna.