November 14, 1860 in Beijing, the Treaty of Beijing was signed between Russia and China, confirming the Aigon and Tianjin treaties and finally defining the eastern border between the possessions of Russia and China.
Since the Aigon Treaty of 1858, the first treaty on the borders of Russia and China, did not delimit the lands from the Ossory River to the sea, in March 1859 the Russian government sent a special mission to Beijing for negotiations headed by General N. P. Ignatiev. On the side of the Qing Dynasty, the Grand Duke Gong took part in the negotiations.
Nikolai Ignatiev, who skillfully played on the contradictions of Chinese and Anglo-French diplomacy, whose representatives negotiated after the end of the Second Opium War, managed to convince the Chinese side that the transfer of the Ossory region to Russia would benefit China, as it would protect against European invasion from the north, from Manchuria. The agreement confirmed the provisions of the Treaty of Aigon and secured the territory of the Ossory region for Russia.
You can understand more about the history of the Beijing Agreement here, here and here.