 Over the course of 250 years, the throne slowly tried to integrate the most strategically and economically important regions—i.e.Lower Burma, Tenasserim, northernmost Irrawaddy valley—into the core by appointing its governors in place of hereditary rulers.In the 12th and 13th centuries, for example, Pagan made a point of appointing its governors in the Tenasserim coast to closely supervise the ports and revenues.