Raj (1931) classified them as an "upper caste", i.e. Dwija, and the final British Raj law case involving their varna in 1926 determined them to be Kshatriya. Earlier, in Bihar, in 1811–1812, botanist and zoologist Francis Buchanan had recorded the Kayastha of that region as "pure shudra" and accordingly kept them at the par with other producer caste groups like goldsmiths, Ahirs, Kurmis and the Koeris. William Pinch, in his study of Ramanandi Sampradaya in the north describes the emergence of the concept of "pure Shudra" in growing need of physical contact with some of the low caste groups who were producer and seller of essential commodities or were the provider of services without which the self sufficiency of rural society couldn't persist. However, many of these adopted Vaishnavism in the aim to become Kshatriya. In 1901 Bihar census, Kayasthas of the area were classified along with Brahmins and Rajputs in Bihar as "other castes of twice-born rank" According to Arun Sinha, there was a strong current since the end of the 19th century among Shudras of Bihar to change their status in caste hierarchy and break the monopoly of bipolar elite of Brahmins and Rajputs of having "dvija" status. The education and economic advancement made by some of the former Shudra castes enabled them to seek the higher prestige and varna status. The Kayastha along with the Bhumihars were first among the shudras to attain the recognition as "upper caste" leaving the other aspirational castes to aspire for the same. The Raj era rulings were based largely upon the theories of Herbert Hope Risley, who had conducted extensive studies on castes and tribes of the Bengal Presidency. According to William Rowe, the Kayasthas of Bengal, Bombay and the United Provinces repeatedly challenged this classification by producing a flood of books, pamphlets, family histories and journals to pressurise the government to recognise them as kshatriya and to reform the caste practices in the directions of sanskritisation and westernisation. Rowe's opinion has been challenged, with arguments that it is based on "factual and interpretative errors", and criticised for making "unquestioned assumptions" about the Kayastha Sanskritisation and westernisation movement. In post-Raj assessments, the Bengali Kayasthas, alongside Bengali Brahmins, have been described as the "highest Hindu castes". After the Muslim conquest of India, they absorbed remnants of Bengal's old Hindu ruling dynastiesincluding the Sena, Pala, Chandra, and Varmanand, in this way, became the