'Rigveda' is an ancient Indian religious book. It is counted as one of the four sacred Hindu writings, which are called Vedas. It is the world's oldest religious writings. It is also one of the oldest writings in Sanskrit language. Rigveda is very important to Hindus, especially Hindus in India and Nepal. Its words are said during prayers and religious gatherings. It is dated up to 4000 years ago but on the basis of astronomical calculations it is dated back to 8000 years and some calculations date back it to 10,000 years.