This fascinating instrument is a relatively new entrant into the world of Indian art music, although the instrument itself is quite old. The Esraj is played mainly in eastern India, in the provinces of Bengal and Bihar. Bishnupur in Bengal and Gaya in Bihar are two great centres where this instrument has been used in art music during the past two hundred years and more. The instrument first came to eastern India in the 12th century AC when Bakhtiyar Khilji came to north Bengal. However, it remained a folk instrument, together with other bowed instruments like the Dilruba (which is to an Esraj what the viola is to the violin), the Sarengi and the Sarinda.
In Indian musicological texts, all stringed instruments are referred to as Veena. Those used in art music in ancient times were of three types: the Vana Veena, the Alavu and the Koormaa. The Vana Veena was a lyre or harp, the Alavu had a gourd at one or both ends and a hollow middle section and was the forerunner of the present day Sitar. The Koormaa was carved out of a single piece of wood and shaped like a tortoise shell (hence the name -- Koormaa literally means "of or like a tortoise") with a leather membrane covering the face. It was the forerunner of the present day Sarod. Contrary to the suggestion of some musicians (not necessarily musicologists but nevertheless commanding popular following on account of being "stars" as performers!), the Sarod was not brought into India by tribals, soldiers, tradesmen or others arriving from sundry regions in the middle east bringing the Rabab from there into India. Rather, the Rabab was just another Koorma that went, like so many other cultural manifestations, from India to those sundry middle eastern regions... Nor was the Santoor, it may be mentioned en passant, ever a "classical" instrument.
Apart from those above, there were the bowed stringed instruments like Ravanhattaa, Sarengi, and Sarinda. These were folk instruments and came under the class of Pinak Veena mentioned in the ancient texts. They began to be used in art music only from about the 16th century AC.
The Esraj was created from a mixture of the Sitar (a fretted and plucked stringed instrument)and the Sarengi (a fretless and bowed stringed instrument). The strings of the Esraj are never pressed so as to touch the frets. Nor do they produce only harmonic tones. They are stopped, but only by a light pressure of the finger. This enables the essential slides (glissandi) and other ornaments without which Indian art music is impossible.
Acharya Dr Chintamani Rath is possibly the sole exponent of this wonderful instrument in the whole of Australasia.