The Sanskrit grammar treatise Ashtadhyayi, composed around 500 BCE by Panini, is said to be the earliest scientific book on Sanskrit grammar. A monumental work of precision, it contains 4,000 rules of grammar in as many sutras expounding a vast array of topics like syntax, root derivatives and moods. (In pic: Birch-bark manuscript from Kashmir of the Rupavatara, a grammatical textbook based on the Sanskrit grammar of Panini. It is said to have been composed by Dharmakirti, a Buddhist monk from Ceylon and the manuscript was transcribed in 1663)