From the time of ancient Indian civilization Raksha Bandhan symbolizes the spiritual bonding between brothers and sisters. Brothers takes oath to protect their sisters and sisters prays to god for safety and well being of their brothers. Raksha Bandhan basically a ritual where sisters tie a string called "Rakhi" in the wrist of their brothers to protect them from evil and wishing them well being. In return brothers prays for sisters and takes oath to protect her.
In 300BC when King Alexander attached India, he stepped back by the heroic effort by the Indian King Puru for the first time. Knowing this Wife of Alexander approached King Puru with Rakhi and King Puru accepted her as sister. After that when next war took place King Puru kept the promise made to her Greek sister and refrained from King Alexander. This is the oldest incident came to know about Raksha Bandhan.
In 15th century the Raksha Bandhan come up with a new dimension when Famous Mughal emperor Humayun got a Rakhi from Rani Karnawatee of Chittor. The incident happens when Bahadur Shah, The Sultan of Gujrat invaded Chittor and just widowed queen of Maharaja of Chittor found no way to defend, she sent a Rakhi to Mughal Badshah Humayun, and touched by the warmth of the brother sister relationship Badshah Humayun marched for Chittor to save Rani Karnawatee.
The most recent reference of Raksha Bandhan as social revolutionary ritual found when in 1905 British empire decided to break Bengal, a state of British India in parts in basis of religion. Kaviguru Rabindra Nath Tagore arranged a ceremony to celebrate Raksha Bandhan to unite both Hindu and Muslim people of Bengal and launch a protest against British empire.
Now a day Raksha Bandhan celebrated as a ritual between brothers and sisters with the same ancient thought of love, well wishing and protection.
The ritual of Raksha Bandhan consists of tieing up Rakhi by sisters on the wrist of the brother. Then sister prays for brothers well being and brother takes oath to protect his sister under and adverse circumstances. After that brother gifts something to sister to mark the occasion.
Raksha Bandhan basically celebrated in full moon called "Rakhi Purnima". In different parts of India Raksha Bandhan celebrated in different names.
In northern and western part of India Rakhi celebrated in "Rakhi Purnima".
In Western Ghats it calls "Nariyel Purnima" to signify the full moon like coconut.
In southern part of the India Rakhi celebrated as "Avani Avittam / Upakarmam".
Central India celebrates it as "Kajari Purnima".
Far western part of the India celebrates it as "Pavitrapana".