How knowledge of weapons (shastra) शस्त्र got lost?

Question

How did the knowledge of great weapons like Bramhastra got lost in Hinduism tradition? As can be seen in Ramayan and Mahabharat, Gurus used to give knowledge of weapons to their shishya which were then used to protect Dharma. But eventually this knowledge was lost and Bharat couldn't fight invaders. How did this happen? Why weren't Devas invoked through yajnas when Sanatan Dharma followers were ethnically cleansed at the rate of millions by foreign invaders? At time of Mahabharat Indra himself helped Arjuna by granting him weapons. What happened now?

Answer 1

Q: How did the knowledge of great weapons like Bramhastra got lost in Hinduism tradition?

Knowledge of great weapons like Brahmastra didn't get lost, they are still existing.

Simple proof is that Parashurama has the knowledge of Brahmasatra and he is a chiranjeevi[1],[2] i.e, he is alive now.

Narada said, 'That tiger of Bhrigu's race (viz., Rama), was well-pleased with the might of Karna's arms, his affection (for him), his self-restraint, and the services he did unto his preceptor. Observant of ascetic penances, Rama cheerfully communicated, with due forms, unto his penance-observing disciple, everything about the Brahma weapon with the mantras for withdrawing it. Having acquired a knowledge of that weapon, Karna began to pass his days happily in Bhrigu's retreat, and endued with wonderful prowess, he devoted himself with great ardour to the science of weapons. One day Rama of great intelligence, while roving with Karna in the vicinity or his retreat, felt very weak in consequence of the fasts he had undergone.

[Section 3, Rajadharmanusasana Parva, Santi Parva, The Mahabharata]

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Q: As can be seen in Ramayan and Mahabharat, Gurus used to give knowledge of weapons to their shishya which were then used to protect Dharma. But eventually this knowledge was lost and Bharat couldn't fight invaders. How did this happen?

In Ramayan and Mahabharat, Gurus didn't give the knowledge of every weapon to every sishya. Inorder to give the knowledge of great weapons, honest guru atleast verify the eligibility of the sishya and sometimes the purpose also. If the sishya is either ineligible or asking weapon for bad purposes then the guru may not give the knowledge of weapon or may revoke it, if given earlier.

In Mahabharata, Drona did not give the knowledge of Brahmastra to Karna

Beholding that Dhananjaya was superior to every one in the science of weapons, Karna. one day approached Drona in private and said these words unto him, 'I desire to be acquainted with the Brahma weapon, with all its mantras and the power of withdrawing it, for I desire to fight Arjuna. Without doubt, the affection thou bearest to every one of thy pupils is equal to what thou bearest to thy own son. I pray that all the masters of the science of weapons may, through thy grace, regard me as one accomplished in weapons!' Thus addressed by him, Drona, from partiality for Phalguna, as also from his knowledge of the wickedness of Karna, said, 'None but a Brahmana, who has duly observed all vows, should be acquainted with the Brahma weapon, or a Kshatriya that has practised austere penances, and no other.' When Drona had answered thus, Karna, having worshipped him, obtained his leave, and proceeded without delay to Rama then residing on the Mahendra mountains.

[Section 2, Rajadharmanusasana Parva, Santi Parva, The Mahabharata]

Parasurama revokes the remembrance of Karna's Brahmasatras knowledge at crucial time

Unto the cheerless and trembling Karna, prostrated with joined hands upon earth, that foremost one of Bhrigu's race, smiling though filled with wrath, answered, 'Since thou hast, from avarice of weapons, behaved here with falsehood, therefore, O wretch, this Brahma weapon shalt not dwell in thy remembrance. Since thou art not a Brahmana, truly this Brahma weapon shall not, up to the time of thy death, dwell in thee when thou shalt be engaged with a warrior equal to thyself! Go hence, this is no place for a person of such false behaviour as thou! On earth, no Kshatriya will be thy equal in battle.' Thus addressed by Rama, Karna came away, having duty taken his leave. Arriving then before Duryodhana, he informed him, saying, 'I have mastered all weapons!'

[Section 3, Rajadharmanusasana Parva, Santi Parva, The Mahabharata]

As I told early, the purpose is also very important. Even the knowledge of weapons won't work if there is no purpose. The presence or absence of weapons solely depends on the purpose only. If there is no purpose then the weapons will be absent i.e., they won't work.

Arjuna's weapons are absent while he was trying to safeguard many people from attacking enemies

"Arjuna said, ‘....... Another incident has happened that is more painful than this, O thou that art possessed of wealth of penances. Repeatedly thinking of it, my heart is breaking. In my very sight, O Brahmana, thousands of Vrishni ladies were carried away by the Abhiras of the country of the five waters, who assailed us. Taking up my bow I found myself unequal to even string it. The might that had existed in my arms seemed to have disappeared on that occasion. O great ascetic, my weapons of diverse kinds failed to make their appearance. Soon, again, my shafts became exhausted. That person of immeasurable soul, of four arms, wielding the conch, the discus, and the mace, clad in yellow robes, dark of complexion, and possessing eyes resembling lotus-petals, is no longer seen by me. .........’

"Vyasa said, ‘......... All this has Time for its root. Time is, indeed, the seed of the universe, O Dhananjaya. It is Time, again, that withdraws everything at its pleasure. One becomes mighty, and, again, losing that might, becomes weak. One becomes a master and rules others, and, again, losing that position, becomes a servant for obeying the behests of others. Thy weapons, having achieved success, have gone away to the place they came from. They will, again, come into thy hands when the Time for their coming approaches. The time has come, O Bharata, for you all to attain to the highest goal. Even this is what I regard to be highly beneficial for you all, O chief of Bharata’s race."

[Section 8, Mausala Parva, The Mahabharata]

Thus possessing of weapons are useful only if time allows it. Else they are useless. So, one need to understand that weapons make their appearances for establishing dharma at proper times by deserved person only.

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Q: Why weren't Devas invoked through yajnas when Sanatan Dharma followers were ethnically cleansed at the rate of millions by foreign invaders? At time of Mahabharat Indra himself helped Arjuna by granting him weapons. What happened now?

As you can see in Arjuna-Vyasa conversation that knowledge of weapons will not be present if some event is destined to happen. Although Arjuna possess knowledge of weapons, weapons did not make their appearance when thousands of Vrishni ladies were carried away by the Abhiras. This is because of the reason that the event need to be happened because of curse. The weapons made their appearances during Kurukshetra war, but not during the above mentioned attack.

Answer 2

Normally, a competent Guru is required to understand a subject at deeper levels. It applies to every branch of knowledge, be it SPIRITUALITY, or science or arts or something else.

Again, a competent Guru will not share all his knowledge to every passerby. He/She should find a suitable disciple, who is competent enough to receive the knowledge.

Sri Ramakrishna Paramahamsa used cry for worthy disciple, while Narendranath (Swami Vivekananda) was searching for a worthy Guru.

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It happens in every branch of science. If one finds the divine weapons mentioned in the Epics like Ramayana or Puranas, but unable to find them in the present age, that situation can indicate innumerable reasons.

For example Sage Viswamitra did not impart his knowledge in divine weapons for every king of his times. He waited for long for the birth of Sri Rama.

A worthy Guru waits for a worthy disciple. That is the underlying principle.

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Drona did not impart all his knowledge in archery to every one. He imparted that knowledge to the Arjuna only. Out of love towards his son Aswathama, he taught the latter the knowledge in Brahmasirsha, which is all powerful, which proved to be detrimental to the mankind.

Competency of disciple includes his/her balance of mind in utilising the knowledge that acquired and searching for a worthy disciple in turn for passing on the knowledge.

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With the elimination of most of the kings in Mahabharata, the society degraded and humans lost the ability to acquire and retain knowledge of great things.

That was how we lost touch with the pure SPIRITUAL concepts of Vedas and got degraded into ritualistic society.

Similar was the case with other branches of knowledge, knowledge of divine weapons being one among them.

Answer 3

Perhaps not exactly the same as Astras (divine weapons), but in some way relevant to the question, are Yantras (mechanical devices). Knowledge regarding mechanical devices (including weaponry) was: 1) regarded as secret knowledge, not to be revealed to just anyone, for this would negate it’s essential effectiveness; and 2) expected to be learned from skilled artisans possessing their own collection of textual sources.

The closest resemblance between Astra and Yantra is possibly the bhūtavāhanayanta, or “mechanical beings animated by a kind of life force” (see bottom of answer).

The mechanical devices included weapons such as mechanical guardians and flying machines, and could be powered by either biological fuel, or some kind of life-force. Besides being aesthetically represented in poetic works of medieval India, they are also dealt with in the 12th century technical manual called the Samaranga-suradhara of king Bhoja.

Whether such weapons actually existed or not, isn't relevant to this discussion. A more important question is if the poetic representations of such fabulous weapons are reflections of that which was written about in technical manuals, or the other way around, i.e., whether the technical manuals (which contain ample instructions on building such devices) were based on descriptions found in poetic literature (which was based on the creative spirit and what was seen with the eye).

The Samaranga-sutradhara dedicates a large section dealing with, among others, mechanical weaponry.

There is a whole category of male and female automata designed for various forms of automatic service (31.101–5), including automata with weapons who serve as guards (31.106–7). There are speaking and dancing birds, dancing horses, monkeys, and elephants (31.73–75).

In his study regarding mechanical devices, Daud Ali states that technical knowledge regarding mechanical deviecs was expected to be in the possession of learned artisans.

It is of course an open question whether any of the machines in the Samarāṅganasūtradhāra were actually made at the courts of medieval Indian kings or were ever made at all. The text is mostly concerned with de-cribing and classifying machines—machines, it claims, that have been ob-served (31.82)—and provides technical knowledge only very sporadically. While the text speaks of specific technologies, like copper piping and elementary hydraulics, it gives no detailed or systematic instructions as to how to construct any of the machines it describes. Like many other śāstras, it presupposes extra-textual knowledge possessed by the craftsman, technician, or machine-maker.

It is also stated the absence of texts containing detailed instructions regarding mechanical devices was not due to the lack of knowledge thereof, but that revealing the secrets one would not attain the desired result:

Bhoja explicitly acknowledges as much—emphasizing that silence on the precise methods of constructing yantras was not due to any ignorance on the matter but rather to maintain secrecy—for without secrecy the fruits (phala) of the machine would not be attained (31.79–80). Wise men were to infer the procedure for making machines from Bhoja’s teaching by using their own intelligence (31.82). Revealing (vyak-tīkṛ) the secrets of machine-making, reasons Bhoja, would neither be in the interests of machine-makers nor give rise to fascination (kautuka) on the part of onlookers (31.81).

In one text (the Bṛhatkathāślokasaṃgraha) it can be found that knowledge regarding mechanical devices should be kept secret in order to guard one’s “way of life”.

At this point a Brahmin tells the story of a certain carpenter of King Mahāsena by the name of Pukvasaka, who once accompanied the king’s en-tourage to Saurashtra, where he was so impressed by the skills of a young artisan by the name of Viśvila that he arranged the young man’s marriage to his daughter, Ratnāvalī, before returning home. Sometime later, Viśvila arrived at Pukvasaka’s home and was married to Ratnāvalī, with whom he fell deeply in love. Almost immediately Viśvila created incredible objects, like special wooden rice kernels that never softened but produced nutritious froth that a man could live on and cooking utensils that prolonged life and prevented disease—all in the manner of the yavanas.
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He then related that Viśvila had been discovered by Brahmadatta’s men in the late watches of the night departing and returning in a kind of large mechanical bird (yantrakukkuṭa). When confronted, Viśvila had pleaded that sin will be incurred and so be it, but as soon as it is discovered, there will be a terrible consequence: the loss of my way of life. For I want to spend my nights in the com-pany of my wife and my days carrying out the king’s orders. Having said this, he implored the king for secrecy.

Mechanical machines were envisioned to be powered by either a source of material fuel, or some sort of life force.

Bhoja mentions flying devices using boiling mercury as a source of fuel:

The ākāśayantra [flying machine], according to Bhoja, was made from light wood, shaped like a giant bird, and flew by the energy generated from vats of boiling mercury. The association of the Bhoja’s preeminent machine with mercury, deemed the most precious and powerful of substances, is perhaps not surprising—mercury would soon become a key ingredient of Bhāskara’s twelfth-century “wheel of perpetual motion.”

More relevant to the discussion on Astras, is the description of mechanical flying machines fueled by some sort of life-force, as mentioned in the Lokapaññati, a 12th century Pali text from Burma:

The Lokapaññati’s rendition of the story begins as a tale of two kingdoms: that of Pāṭaliputta (Sanskrit: Pātaliputra ) and the distant land of “Roma.” Roma, according to the story, was filled with makers of automata—what the text calls literally “machines that were the vehicles of spirits,” bhūtavāhanayanta, or mechanical beings animated by a kind of life force. In Roma, these machines carried out many functions, like commerce (buying and selling), agriculture, and protection. The secrets of this technology were fiercely guarded, and the machine-makers (yantakāras) of Roma were expected to report periodically to the royal court. If there was any prolonged absence, an automaton was sent to hunt down and kill the errant artisan, preventing the knowledge from spreading to other realms.

These specific yantras were capable of flying and acting as intelligent weaponry:

The king of Roma devised a plan, and a metal chest containing an automaton with a sword was dispatched to Pāṭaliputta with messengers who announced that it was a chest full of gems for the emperor. Asoka, curious, called the son of the machine-maker to ex-amine the chest. After examining it carefully, he concluded that it was a trap and that inside the chest was an automaton that had been sent to kill him. He informed the emperor of this but the emperor, influenced by his ministers, remained unconvinced and commanded the artisan to open the box. The artisan, first taking leave to bid farewell to his family, returned and opened the box. As he predicted, an automaton emerged, cut off his head, and then miraculously flew back to Roma. Asoka praised the artisan and blamed his ministers. And here the story ends.

In his final words, he also states that mention of such mechanical devices in literary sources, should not be regarded as an attempt to “explain the magical”:

This “importation” was not some sort of demystification, a case of the machine “explaining” the magical. Unlike post-Renaissance European contexts that tend to begin from the tacit assumption of an opposition between artifice and nature or between science and imagination, our sources present us with a somewhat different mental mapping, where artifice supplemented and completed nature and where mechanics and magic would seem to converge on an aesthetics of wonder. If anything, the magical and mechanical were mutually enhancing.