During the 7th century AD, a settled community known as Vijayapura, a tributary to the Srivijaya empire, was thought to have existed in northwest Borneo. The earliest independent kingdom in Borneo, supposed to have existed from the 9th century, was Po Ni, as recorded in the Chinese geographical treatise "Taiping Huanyu Ji". It was believed that Po Ni existed at the mouth of Brunei River and was the predecessor to the Bruneian Empire. As China had been under the conquest of Mongol Empire, all Chinese vassal state subsequently controlled by the Mongol emperors of China. Early in 1292, Kublai Khan is said to have sent an expedition to northern Borneo, before departing for the invasion of Java in 1293. As a result of this campaign, it is believed that many of his followers in addition to other Chinese traders eventually settled and established their own enclave at Kinabatangan River.