Hinduism, the world's oldest major religion, developed on the Indian subcontinent in the Indus River valley.
This religion sprang up about three thousand years ago and is still practiced by 80 percent of India's population.
According to Hindu tradition, the course of people's lives and their place in society were determined at birth.
What jobs they would perform, whom they would marry, what foods they would eat, and what customs they would follow were all already decided, based on their family's lineage and traditional occupations.
As a result, society was divided into classes in a hierarchy called the "caste" system.
Some historians think the system was introduced when the Aryans, a powerful nomadic tribe, migrated to the Indus Valley around 1500 BC.
When this group settled in the area, they added their gods to the existing religious beliefs and established the caste system.
The creation of the castes is described in a poem in the Rigveda, an ancient and sacred Hindu book.
It explains that a giant named Purusha sacrificed and dismembered himself to make the world.
The Brahman caste came from his head, the Kshatriya caste from his arms, the Vaishya caste from his stomach, and the Sudra caste from his feet.
Each caste had different rights and duties. For society to function, every individual within the caste system had to do his or her job correctly.
In the highest caste were the Brahmans. They were the priests and teachers of society and provided for the intellectual and spiritual needs of the community.
Second in rank were the members of the Kshatriya caste—the warriors and rulers. They were the leaders and protectors of society.
Next in the hierarchy was the Vaishya caste. People of this class were merchants and farmers and formed a sort of middle class.
At the bottom of the caste system were the Sudras—servants and workers. Their function in society was to work as laborers for the other castes.
People of this class could not study religious texts or get a formal education.
Even though most of their lives were spent in hard labor, the Sudras were taught not to struggle against their difficult role in society.
There was, however, an even lower position in Hindu society, occupied by the "untouchables."
These people were considered so low that they remained outside the caste system.
Untouchables performed the "dirty" jobs that no one else wanted to perform, those dealing with blood, dirt, or death.
It was believed they could contaminate the "clean" castes just by looking at them.
As a result, strict rules were put in place to protect others from their "pollution."
Untouchables could not remain on a path if someone from a clean caste approached; nor could they drink water from the same wells.
They were also forbidden to wear shoes in the presence of members of the clean castes, to learn to read or write, or to worship in temples.
Inequalities among the castes were, however, considered natural because they were decreed by the gods.
It was thought that each person within the caste system had been assigned the position in society that he or she deserved.
Movement up to a higher caste had to be earned.
The belief in reincarnation—the concept that the spirit is reborn and returns to life after death again and again—is central to the Hindu way of life.
The caste a person is born into is determined by that person's "karma."
Karma is the sum of the good and bad deeds that an individual has committed throughout his or her lifetimes.
It was assumed that people in the lower castes must have committed many evil deeds to be born into their positions.
But hard work and acceptance of their status throughout life would allow people to come back in a higher caste in their next life.
For instance, a warrior who performed many good deeds in his lifetime might become a priest in his next life.
On the other hand, if someone tried to break free of his or her caste by changing professions, that person could be punished by being reborn into a lower caste.
Over the centuries, many millions of India's underprivileged citizens, who lived on the fringes of society, had no hope of improving their lives or the lives of their children.
Beginning in the 1930s, religious leader Mahatma Gandhi fought to change the patterns of oppression that had been a part of Indian culture for centuries.
He gave untouchables a new name—Harijans, which means "children of God."
In protest of the inequalities they faced, he stated, "I would far rather that Hinduism died than that untouchability lived."
Discrimination based on caste and the concept of "untouchability" was outlawed in India's constitution of 1950.
Since then, improved access to education and other resources has allowed many Harijans to learn to fight for their rights and take their places alongside workers of all different backgrounds.
The boundaries of class are slowly disappearing, and some Harijans now hold positions of power and wealth.
However, the caste system is still present in many areas of modern Indian society.
Many villages are still segregated along caste lines, and some children are still divided according to caste in the classrooms of their primary schools.
At one special time of the year, however, all caste distinctions are set aside.
This occurs at the beginning of every spring during a festival called "Holi."
Also known as the Festival of Colors, this Indian celebration can last for days and includes bonfires, music, dancing, and feasting.
The festival is celebrated today as a way to recognize and embrace the diversity of all people.
People soak themselves, friends, and strangers in colored water and paint themselves with herbal powders called gulal.
All members of society mix freely, because the vibrant colors provide a disguise for everyone, and the strict code of conduct surrounding the castes is forgotten.
This holiday, celebrated for thousands of years, is the one time when India's rigid customs are ignored.
In India's modern society, many traditions and rules are now being questioned. Social and economic changes have begun and will continue.
A booming middle class includes highly educated children who wish to become a part of a global culture.
Although the caste system is still a significant part of Hindu life, many Hindus are now challenging its restrictions.
