evidence: The dynamics and volatility of the border region also made earlier geographic records hardly comprehensive, let alone entirely reliable. Over time tribes migrated, topographical marks changed, and towns and garrisons relocated. For instance, between the early and late fifteenth century the locations of the Jurchen tribe led by Möngke Temür and the border garrisons of Hoeryŏng were recorded quite inconsistently in the Annals of the Chosŏn Dynasty due to the gradual northward extension of the Chosŏn territory and the retreat of the Jurchen.Footnote 13 Nokt’undo, a small island of approximately 32 square kilometers originally located at the estuary of the Tumen River, exemplifies the challenge of topographic changes. It had been Korean territory since the late fifteenth century. But, with constant changes in the canal and sand sediment, the island gradually adjoined the north shore and eventually became part of the Qing side of the riverbank. When Russia forced the Qing to yield the territory of Outer Manchuria, including 15 kilometers of the Tumen River estuary, in 1860, former Nokt’undo Island was transferred to Russia altogether. [...] Between the two rounds of Qing–Chosŏn border negotiations, in 1886, the Qing conducted another demarcation over the Tumen border, with Russia. The context for the Qing–Russian negotiation dates back to the late seventeenth century, when the Russians invaded the Amur River region and Qing troops besieged Fort Yaksa (R. Albazin) and forced Russia to negotiate. Representatives from both sides met at Nerchinsk (C. Nibuchu) in the autumn of 1689. After furious debates and struggles, the two sides reached an agreement defining the eastern section of the border.