Naranarayan (reign 1554–1587) was the last ruler of the undivided Koch dynasty of Kamata Kingdom. He succeeded his father, Biswa Singha. Under him the Koch kingdom reached its cultural and political zenith. Under his rule, and under the military command of his brother Chilarai, he was able to subjugate the entire Brahmaputra valley, including the Ahom kingdom; besides the Kachari, Tripura kingdoms, as well as the Khyrem, Jaintia and others. This influence was halted when he faced Suleman Karranni, the Sultan of Bengal. Naranarayan employed eminent scholars and poets to translate the Bhagavada, the Puranas, and the Mahabharata into Assamese, and to compile the treatise on arithmetic, astronomy, and grammar. The laborious works of the scholars were widely circulated among the people of the country as a result of which even women and Shudras became learned He introduced a silver coin, called the Narayani, that greatly influenced the numismatics of Assam. Ascension At the time of his father's death, Naranaryan and his step brother, Chilarai, were in Varanasi and another brother, Nara Singha, succeed the throne. Malladev, as he was then known, hastened back with Chilarai and with the help of their supporters among the courtier, took over the throne. Nara Singha was pursued, who escaped first to the Morung kingdom, and thence to Nepal and finally Kashmir. Malladev ascended the throne in 1540, in the same year that his father had died, and acquired the title Narayana, which was to become the dynastic title of his succeeding kings. He issued coins, and his seal was made. He appointed his step-brother Chilarai (then known as Sukladhwaj) the yuvaraj (somewhat akin to "prime minister") and the commander-in-chief of the military. Kingdom expansion The Koch kingdom was a tributary the eastern Ahom kingdom and soon after his ascension began preparing to throw off the vassalage. A border tiff at Sala, just above Kaliabor escalated in 1546 with three step-brothers forging ahead into the Ahom kingdom, to meet with their deaths. After a series of battles with varying fortunes, the Koch army was defeated by the Ahoms, then under Suklenmung (1539–1552) who personally led the military, at the Battle of Pichala in 1547. This was followed by a period of calm and preparation. Preparations The preparations for a push east was made slowly and deliberately. After the reverses of Biswa Singha in 1547 due to logistics, and his own in 1547, he made