Will power: two princes who renounced worldly goods and sought spiritual enlightenment

Siddhartha Gautama, the first of these important figures in the history of Indian religions, was an prince called who is thought to have lived in India from about 563BCE to 483BCE. The only historical evidence of his life comes from texts written by his followers some 400 years after his death, so some of the details may well have merged into myth over centuries of oral rendition.

He was born in Lumbini, in modern-day Nepal. His mother, Queen Maya, died a few days after his birth, leaving him to be brought up by his father, Suddhodana, a king or tribal chief, who had three palaces built in honour of his newborn son. His father wanted to shield Siddhartha from religious teaching and knowledge of human suffering, thinking that this would allow him to become a strong king.

But, at the age of 29, Siddhartha left his palaces to meet his subjects. His father tried in vain to remove all signs of poverty and suffering, but to no avail. On his first outing Siddhartha saw an old man – until then he knew nothing of the trials of old age. On further visits he met diseased and dying people. Greatly disturbed by what he had seen, Siddhartha fled from the luxuries of his palaces to live as a monk, begging for food in the streets. He then became a hermit and, with the help of two teachers, learnt how to meditate and to still his mind.

Next, Siddhartha and five companions tried to find enlightenment by the total denial of all worldly goods, including food – at one time they ate no more than a single leaf or nut a day. After collapsing in a river and nearly drowning, Siddhartha discovered what came to be known as the "Middle Way" – a path towards enlightenment (liberation of the atman) that could be accomplished without the need for extremes, whether of self-indulgence or self-denial.

After receiving the gift of some rice pudding from a village girl, Siddhartha sat under a tree until he found the Truth. After 49 days of meditation, aged 35, he at last attained enlightenment, and from then on became known as the Buddha, meaning "awakened one".

For the next 45 years the Buddha journeyed by foot around the plain of the Ganges River, in north-east India and southern Nepal, teaching his doctrine to a wide range of people, from royalty to terrorists and beggars. After making thousands of converts, he died at about the age of 80, perhaps of food poisoning.

Buddha's teachings were really an extension, or popular interpretation, of many traditional Hindu beliefs. They were of enormous appeal, especially to the poor, for whom there was little hope of social or material improvement. The Buddha explained how by following his "Four Noble Truths" and the "Noble Eightfold Path", these people could rid themselves of inner desires and free their spirits to eternal liberation without the involvement of any priest, king or other intermediary.

Another prince who lived at about the same time as Gautama also renounced his kingdom, and is said to have attained spiritual enlightenment after wandering for 12-and-a-half years in deep silence and meditation. This man was known as Mahavira, meaning "great hero", and he became the 24th and last prophet ( tirthankar) of the Jain religion.

Jain scriptures were written over a long period of time, but the most popular work was written by an Indian monk called Umaswati more than 1,800 years ago. In his Tattvartha Sutra, or Book of Reality, the main aspects of Jainism are set out, identifying its central belief that all life, both human and non-human, is sacred.

For Jains, there is no justification for killing another person, however greatly provoked or threatened. They refuse all food obtained by unnecessary cruelty. Jains are vegetarians and avid supporters of animal welfare. In many Indian towns today animal shelters are run by Jain people. Root vegetables are avoided, as harvesting them destroys an entire plant, whereas fruit, such as an apple, is acceptable, as picking it will leave the tree unharmed.

Non-violence, religious toleration and respect for nature are cornerstones of the Jain philosophy, which, like Hinduism and Buddhism, is concerned with liberating the individual's soul through enlightenment accomplished through a series of codes of conduct that involve taking five vows: of non-violence to all living things ( ahimsa); truthfulness ( satya); non-stealing ( asteya); chastity ( brahmacharya); and detachment from material possessions ( aparigraha).

Beyond war: two rulers who taught the idea of living at peace with man and nature

Neither Buddhism nor Jainism would have had nearly such a big impact on human history were it not for the patronage of certain rulers in the secular world. By about 500BCE, 16 different kingdoms, known as the Mahajanapadas, divided the Indian subcontinent, from modern-day Afghanistan in the west, to Bangladesh in the east.

Most of these kingdoms were consolidated into India's first empire by Chandragupta Maurya who ruled c320BCE to c298BCE. Unlike the Chinese example, India's itch to centralise was less to do with internal power struggles between kingdoms and more a response to threats from outside, in the form of Persian and Greek armies that, from about 500BCE, started harassing Indian frontiers, especially in the north-west. By 303BCE, Chandragupta is reputed to have had an army of some 600,000 men, with 30,000 cavalry and 9,000 elephants. But towards the end of his life he gave it all up and became a Jain monk. Eventually, it is said, he starved himself to death in a cave.

While Chandragupta established the Jain religion as the preferred philosophy of the most powerful ruling family in India, it was his grandson who had the biggest impact of all. Ashoka the Great, who ruled from 273BCE to 232BCE was, to begin with, as ruthless and violent as any imperial monarch, controlling his empire through the threat of force. Indeed, the name Ashoka means "without sorrow" in Sanskrit.

But, shortly after the end of one of the biggest and bloodiest wars of the time, he underwent a profound and complete conversion. The Kalinga War ( c265BCE–263BCE) ended with the famous Battle of Kalinga, which left more than 100,000 people dead on the battlefield. On the day after the battle, Ashoka walked out across the city where, as far as his eye could see, the only sights were burnt-out houses, dead horses and scattered bodies. "What have I done?" he cried.

From that moment on Ashoka is said to have devoted his life and his reign to non-violence. He became a devout Buddhist and over the next 20 years dedicated himself to spreading the message of this powerful religion. Prisoners were freed and given back their land. Ahimsa, the Buddhist doctrine of non-violence, was adopted throughout his domains, forbidding the unnecessary slaughter of animals. Hunting for sport was banned, branding animals was outlawed and vegetarianism was encouraged as official policy.

Ashoka built rest-houses for travellers and pilgrims, universities so people could become more educated, and hospitals for people and animals alike throughout India. As many as 84,000 monuments and monasteries ( stupas and viharas) were erected for Buddhist followers, many of them built at places associated with the life of the Buddha.

His most lasting legacy is probably the Edicts, which were engraved on the dozens of sandstone pillars that were erected throughout what is now Pakistan and northern India. Written in the widely spoken language of the ordinary people, Prakrit, they popularised Ashoka's beliefs in the Buddhist concept of righteousness ( dharma). Their inscriptions provide details of his conversion after the Battle of Kalinga, as well as his policy of non-violence towards all living things: "I have made provision for two types of medical treatment. One for humans and one for animals. Wherever medical herbs suitable for humans and animals are not available, I have had them imported and grown... Along roads I have had wells dug and trees planted for the benefit of humans and animals." (Rock Edict number 2.)

Ashoka sent missionaries to every king and court he could. He wanted everyone to know about the Buddha's message. They travelled as far as Greece, Lebanon, Egypt, Burma and Sri Lanka. The first Egyptian Buddhist colonies in Alexandria date from this time. Ashoka promoted a new notion of kingship, in which a ruler's legitimacy was gained not from the generosity of a divine god, but by advocating Buddhist ideals, establishing monasteries, supporting monks and promoting conflict resolution.

Following Ashoka's reign, Buddhism spread far and wide. His twin children Mahindra and Sanghamitra settled in Sri Lanka, converting its rulers and people to Buddhism.

By 100CE, Buddhist monks had established a foothold in China, where their teaching fused with a similar philosophy called Taoism, founded by a philosopher called Laozi who lived at the time of the Hundred Schools of Thought. His book, called the Tao Te Ching, described how violence should be avoided at all costs, and how individuals should rid themselves of strong emotions and desires through stillness and meditation. (It is ironic that in an attempt to find an elixir for immortality in c850CE, Taoist monks discovered how to make gunpowder.)

Ashoka's influence now looks more powerful beyond India than within it because, by about 1300CE, Buddhism in India had declined into a relatively minor religion, marginalised by a resurgence of Hinduism and the onset of Islam.

From China, various brands of Buddhism spread to Korea, Vietnam and Thailand. By 538CE its message had reached the islands of Japan, and, by the ninth century, Borobudur, in Java, where an immense cluster of Buddhist temples remains to this day. The shrines of Angkor Wat in Cambodia were built 300 years later which, although Hindu in inspiration, include extensive Buddhist sculptures. This religious complex, the apex of a highly religious civilisation, is now buried deep in the jungle, spread across 40 square miles.

The brightest modern example of a Buddhist kingship takes us back up into the Himalayas. Today the kingdom of Bhutan, nestled high in the mountains, is home to just over 650,000 people. A Buddhist monk called Padmasambhava is reputed to have brought the Buddha's teachings to Bhutan and Tibet in 747CE.

Jigme Singye Wanngchuck, fourth King of Bhutan, who ruled 1972–2006, stated that Gross National Happiness is more important to his people than Gross National Product – putting the concerns of social welfare, environmental preservation and cultural protection above economic growth.

In a unique echo of Ashoka's edicts, the small, spiritual society of Bhutan is today still attempting to place material and spiritual well-being alongside the preservation of the natural environment.